The blog of LCR: objectiveC

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Looking to start creating your first iOS application? Then check out this awesome tutorial: <a href="http://ios-blog.co.uk/tutorials/create-your-first-ios-7-hello-world-application/?utm_source=CheatSheetInternal&utm_medium=CheatSheetInternal&utm_term=CheatSheetInternal&utm_content=CheatSheetInternal&utm_campaign=CheatSheetInternal" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Create your first iOS 7 Hello World Application</a><br />-</div>
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Note: I wrote this over a stretch of 3 days, so it could probably use some editing and clarifications where necessary, Leave a comment below with any suggestions and alterations.</div>
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This is not meant to be a beginner’s guide or a detailed discussion about Objective-C; it is meant to be a quick reference to common, high level topics.</div>
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If something isn’t mentioned here, it’s probably covered in detail in one of these:</div>
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– <a href="http://ios-blog.co.uk/tutorials/beginners-ios-development-objective-c//?utm_source=internalLink&utm_medium=internalLink&utm_term=internalLink&utm_content=internalLink&utm_campaign=internalLink" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Objective-C: A Comprehensive Guide for Beginners</a><br />– <a href="http://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/ObjectiveC/Introduction/introObjectiveC.html" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">The Objective-C Programming Language</a><br />– <a href="https://developer.apple.com/library/mac/#documentation/Cocoa/Conceptual/CodingGuidelines/CodingGuidelines.html" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">Coding Guidelines for Cocoa</a><br />– <a href="http://developer.apple.com/library/ios/#documentation/iphone/conceptual/iphoneosprogrammingguide/Introduction/Introduction.html" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">iOS App Programming Guide</a></div>
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Table of Contents</h3>
<ul class="disc" style="background-color: white; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; list-style-image: initial; list-style-position: outside; margin: 0px 0px 20px 30px; padding: 0px; vertical-align: baseline;">
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#commenting" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Commenting</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#data-types" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Data Types</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#constants" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Constants</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Operators</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#declaring-classes" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Declaring Classes</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#preprocessor-directives" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Preprocessor Directives</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#compiler-directives" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Compiler Directives</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#literals" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Literals</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#methods" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Methods</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#properties-and-variables" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Properties and Variables</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#naming-conventions" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Naming Conventions</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#blocks" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Blocks</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#control-statements" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Control Statements</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#enumeration" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Enumeration</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#extending-classes" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Extending Classes</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#error-handling" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Error Handling</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#passing-information" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Passing Information</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#user-defaults" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">User Defaults</a></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#common-patterns" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Common Patterns</a></li>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#commenting" name="commenting" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Commenting</h3>
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Objective-C Comments should be used to organize code and to provide extra information for future refactoring or for other iOS developers who might be reading your code. Comments are ignored by the compiler so they do not increase the compiled program size.</div>
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Two ways of commenting:</div>
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// This is an inline comment

/* This is a block comment
   and it can span multiple lines. */

// You can also use it to comment out code
/*
- (SomeOtherClass *)doWork
{
    // Implement this
}
*/</div>
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Using <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">pragma</strong> to organize your code:</div>
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#pragma mark - Use pragma mark to logically organize your code

// Declare some methods or variables here

#pragma mark - They also show up nicely in the properties/methods list in Xcode

// Declare some more methods or variables here</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#data-types" name="data-types" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Data Types</h3>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#size" name="size" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Size</h4>
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Permissible sizes of data types are determined by how many bytes of memory are allocated for that specific type and whether it’s a 32-bit or 64-bit environment. In a 32-bit environment, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">long</strong> is given 4 bytes, which equates to a total range of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">2^(4*8)</strong> (with 8 bits in a byte) or <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">4294967295</strong>. In a 64-bit environment, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">long</strong> is given 8 bytes, which equates to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">2^(8*8)</strong> or<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">1.84467440737096e19</strong>.</div>
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For a complete guide to 64-bit changes, please <a href="https://developer.apple.com/library/mac/documentation/Darwin/Conceptual/64bitPorting/transition/transition.html#//apple_ref/doc/uid/TP40001064-Ch307-TPXREF101" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">see the transition document</a>.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#c-primitives" name="c-primitives" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>C Primitives</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Note:</strong> Objective-C inherits all of the C language primitive types and then adds a few extras.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#void" name="void" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Void</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">void</strong> is C’s empty data type. It is most commonly used to specify the return type for functions that don’t return anything.</div>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#integers" name="integers" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Integers</h4>
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Integers can be signed or unsigned. When signed, they can be either positive or negative and when unsigned, they can only be positive. Example: When declaring an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">unsigned int</strong>, the range of allowable integer values for a 32-bit compiler will shift from -2147483648 to +2147483647 to instead be 0 to +4294967295.</div>
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Integer types with their accompanying byte sizes:</div>
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// Char (1 byte for both 32-bit and 64-bit)
unsigned char anUnsignedChar = 255;
NSLog(@"char size: %zu", sizeof(char));

// Short (2 bytes for both 32-bit and 64-bit)
short aShort = -32768;
unsigned short anUnsignedShort = 65535;
NSLog(@"short size: %zu", sizeof(short));

// Integer (4 bytes for both 32-bit and 64-bit)
int anInt = -2147483648;
unsigned int anUnsignedInt = 4294967295;
NSLog(@"int size: %zu", sizeof(int));

// Long (4 bytes for 32-bit, 8 bytes for 64-bit)
long aLong = -9223372036854775808; // 32-bit
unsigned long anUnsignedLong = 18446744073709551615; // 32-bit
NSLog(@"long size: %zu", sizeof(long));

// Long Long (8 bytes for both 32-bit and 64-bit)
long long aLongLong = -9223372036854775808;
unsigned long long anUnsignedLongLong = 18446744073709551615;
NSLog(@"long long size: %zu", sizeof(long long));</div>
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Fixed width integer types with their accompanying byte sizes as the variable names:</div>
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// Exact integer types
int8_t aOneByteInt = 127;
uint8_t aOneByteUnsignedInt = 255;
int16_t aTwoByteInt = 32767;
uint16_t aTwoByteUnsignedInt = 65535;
int32_t aFourByteInt = 2147483647;
uint32_t aFourByteUnsignedInt = 4294967295;
int64_t anEightByteInt = 9223372036854775807;
uint64_t anEightByteUnsignedInt = 18446744073709551615;

// Minimum integer types
int_least8_t aTinyInt = 127;
uint_least8_t aTinyUnsignedInt = 255;
int_least16_t aMediumInt = 32767;
uint_least16_t aMediumUnsignedInt = 65535;
int_least32_t aNormalInt = 2147483647;
uint_least32_t aNormalUnsignedInt = 4294967295;
int_least64_t aBigInt = 9223372036854775807;
uint_least64_t aBigUnsignedInt = 18446744073709551615;

// The largest supported integer type
intmax_t theBiggestInt = 9223372036854775807;
uintmax_t theBiggestUnsignedInt = 18446744073709551615;</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#floating-point" name="floating-point" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Floating Point</h4>
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Floats cannot be signed or unsigned.</div>
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// Single precision floating-point (4 bytes for both 32-bit and 64-bit)
float aFloat = 72.0345f;
NSLog(@"float size: %zu", sizeof(float));

// Double precision floating-point (8 bytes for both 32-bit and 64-bit)
double aDouble = -72.0345f;
NSLog(@"double size: %zu", sizeof(double));

// Extended precision floating-point (16 bytes for both 32-bit and 64-bit)
long double aLongDouble = 72.0345e7L;
NSLog(@"long double size: %zu", sizeof(long double));</div>
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<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#objective-c-primitives" name="objective-c-primitives" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Objective-C Primitives</h3>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">id</strong> : Known as the anonymous or dynamic object type, it can store a reference to any type of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">object</strong> with no need to specify a pointer symbol.</div>
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id delegate = self.delegate;</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Class</strong> : Used to denote an object’s class and can be used for introspection of objects.</div>
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Class aClass = [UIView class];</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Method</strong> : Used to denote a method and can be used for swizzling methods.</div>
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Method aMethod = class_getInstanceMethod(aClass, aSelector);</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">SEL</strong> : Used to specify a selector which is compiler-assigned code that identifies a method name.</div>
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SEL someSelector = @selector(someMethodName);</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">IMP</strong> : Used to point to the memory address of the start of a method. You will probably never need to use this.</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 540px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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IMP theImplementation = [self methodForSelector:someSelector];</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">BOOL</strong> : Used to specify a boolean type where <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">0</strong> is considered <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NO</strong> (false) and any non-zero value is considered <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">YES</strong> (true). Any <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">nil</strong> object is also considered to be <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NO</strong> so there is no need to perform an equality check with<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">nil</strong> (e.g. just write <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if (someObject)</strong> not <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if (someObject != nil)</strong>).</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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// Boolean
BOOL isBool = YES; // Or NO</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">nil</strong> : Used to specify a null object pointer. When classes are first initialized, all properties of the class are set to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">0</strong> which means they point to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">nil</strong>.</div>
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Objective-C also has a number of other types such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSInteger</strong>,<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSUInteger</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">CGRect</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">CGFloat</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">CGSize</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">CGPoint</strong>, etc.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#enum--bitmask-types" name="enum--bitmask-types" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Enum & Bitmask Types</h3>
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Objective-C Enumeration types can be defined a number of different ways:</div>
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// Specifying a typed enum with a name (recommended way)
typedef NS_ENUM(NSInteger, UITableViewCellStyle) {
    UITableViewCellStyleDefault,
    UITableViewCellStyleValue1,
    UITableViewCellStyleValue2,
    UITableViewCellStyleSubtitle
};

// Specify a bitmask with a name (recommended way)
typedef NS_OPTIONS(NSUInteger, RPBitMask) {
    RPOptionNone      = 0,
    RPOptionRight     = 1 << 0,
    RPOptionBottom    = 1 << 1,
    RPOptionLeft      = 1 << 2,
    RPOptionTop       = 1 << 3
};

// Other methods:

// Untyped
enum {
    UITableViewCellStyleDefault,
    UITableViewCellStyleValue1,
    UITableViewCellStyleValue2,
    UITableViewCellStyleSubtitle
};

// Untyped with a name
typedef enum {
    UITableViewCellStyleDefault,
    UITableViewCellStyleValue1,
    UITableViewCellStyleValue2,
    UITableViewCellStyleSubtitle
} UITableViewCellStyle;</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#casting-to-data-types" name="casting-to-data-types" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Casting to Data Types</h3>
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Sometimes it is necessary to cast an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">id</strong> or different type into a specific class or data type. Examples of this would be casting from a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">float</strong> to an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">int</strong> or from a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITableViewCell</strong> to a subclass such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">RPTableViewCell</strong>.</div>
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Casting non-object data types:</div>
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<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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// Format: nonObjectType variableName = (nonObjectType)variableNameToCastFrom;
int anInt = (int)anAnonymouslyTypedNonObjectOrDifferentDataType;</div>
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Casting object data types:</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 844px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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// Format: ClassNameOrObjectType *variableName = (ClassNameOrObjectType *)variableNameToCastFrom;
UIViewController *aViewController = (UIViewController *)anAnonymouslyTypedObjectOrDifferentDataType;</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#constants" name="constants" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Constants</h3>
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Using <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">const</strong> is usually the better approach since <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">const</strong> points to the same memory address for any references to that item in code. <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">#define</strong> defines a macro which replaces all references with the actual constant value contents before compilation starts, instead of being a memory pointer to that constant value.</div>
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Objective-C Constants can be defined as:</div>
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5</div>
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// Format: type const constantName = value;
NSString *const kRPShortDateFormat = @"MM/dd/yyyy";

// Format: #define constantName value
#define kRPShortDateFormat @"MM/dd/yyyy"</div>
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To make the constant available to external classes, you must also add it to the header <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.h</strong> file:</div>
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1</div>
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extern NSString *const kRPShortDateFormat;</div>
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If you know that a constant will only be available within it’s containing implementation <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.m</strong> file, specify it as:</div>
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1</div>
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static NSString *const kRPShortDateFormat = @"MM/dd/yyyy";</div>
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A static variable declared within a method retains its value between invocations. This can be useful when declaring a <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#singletons" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">singleton</a> or creating custom setters/getters for a property.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#operators" name="operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Operators</h3>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#arithmetic-operators" name="arithmetic-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Arithmetic Operators</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Operator</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
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<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">+</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Addition</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">-</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Subtraction</td></tr>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#relational-and-equality-operators" name="relational-and-equality-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Relational and Equality Operators</h4>
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<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">==</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Equal to</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">!=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Not equal to</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Greater than</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Less than</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">>=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Greater than or equal to</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Less than or equal to</td></tr>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#logical-operators" name="logical-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Logical Operators</h4>
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<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Operator</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">!</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">NOT</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">&&</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Logical AND</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">||</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Logical OR</td></tr>
</tbody></table>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#compound-assignment-operators" name="compound-assignment-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Compound Assignment Operators</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Operator</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">+=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Addition</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">-=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Subtraction</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">*=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Multiplication</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">\/=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Division</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">\%=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Modulo</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">&=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Bitwise AND</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">|=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Bitwise Inclusive OR</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">^=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Exclusive OR</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><<=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Shift Left</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">>>=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Shift Right</td></tr>
</tbody></table>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#increment-and-decrement-operators" name="increment-and-decrement-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Increment and Decrement Operators</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Operator</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">++</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Addition</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">–</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Subtraction</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">*=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Multiplication</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">/=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Division</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">%=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Modulo</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">&=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Bitwise AND</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">|=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Bitwise Inclusive OR</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">^=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Exclusive OR</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><<=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Shift Left</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">>>=</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Shift Right</td></tr>
</tbody></table>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#bitwise-operators" name="bitwise-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Bitwise Operators</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Operator</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">&</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Bitwise AND</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">|</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Bitwise Inclusive OR</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">^</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Exclusive OR</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">~</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Unary complement (bit inversion)</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><<</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Shift Left</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">>></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Shift Right</td></tr>
</tbody></table>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#other-operators" name="other-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Other operators</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Operator</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">()</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Cast</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">? :</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Conditional</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">&</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Memory Address</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">*</td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Pointer</td></tr>
</tbody></table>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#declaring-classes" name="declaring-classes" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Declaring Classes</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Classes are declared using two files: a header ( <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.h</strong>) file and an implementation ( <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.m</strong>) file.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
The header file should contain (in this order):</div>
<ul class="disc" style="background-color: white; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; list-style-image: initial; list-style-position: outside; margin: 0px 0px 20px 30px; padding: 0px; vertical-align: baseline;">
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Any needed <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">#import</strong> statements or forward <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@class</strong> declarations</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Any protocol declarations</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@interface</strong> declaration specifying which class you’re inheriting from</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">All publicly accessible variables, properties and methods</li>
</ul>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
The implementation file should contain (in this order):</div>
<ul class="disc" style="background-color: white; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; list-style-image: initial; list-style-position: outside; margin: 0px 0px 20px 30px; padding: 0px; vertical-align: baseline;">
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Any needed <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">#import</strong> statements</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">An anonymous category, or class extension, for any private variables or properties</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@implementation</strong> declaration specifying the class</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">All public and private methods</li>
</ul>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Example:</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
MyClass.h</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 716px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
#import "SomeClass.h"

// Used instead of #import to forward declare a class in property return types, etc.
@class SomeOtherClass;

// Place all global constants at the top
extern NSString *const kRPErrorDomain;

// Format: YourClassName : ClassThatYouAreInheritingFrom
@interface MyClass : SomeClass

// Public properties first
@property (readonly, nonatomic, strong) SomeClass *someProperty;

// Then class methods
+ (id)someClassMethod;

// Then instance methods
- (SomeOtherClass *)doWork;

// Declare any constants at the top
NSString *const kRPErrorDomain = @"com.myIncredibleApp.errors";
static NSString *const kRPShortDateFormat = @"MM/dd/yyyy";

// Class extensions for private variables / properties
@interface MyClass ()
{
    int somePrivateInt;

// Re-declare as a private read-write version of the public read-only property
    @property (readwrite, nonatomic, strong) SomeClass *someProperty;
}
@end

@implementation MyClass

// Use #pragma mark - statements to logically organize your code
#pragma mark - Class Methods

+ (id)someClassMethod
{
    return [[MyClass alloc] init];
}

#pragma mark - Init & Dealloc methods

- (id)init
{
    if (self = [super init]) {
        // Initialize any properties or setup code here
    }

return self;
}

// Dealloc method should always follow init method
- (void)dealloc
{
    // Remove any observers or free any necessary cache, etc.

[super dealloc];
}

#pragma mark - Instance Methods

- (SomeOtherClass *)doWork
{
    // Implement this
}

@end</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#instantiation" name="instantiation" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Instantiation</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
When you want to create a new instance of a class, you use the syntax:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
MyClass *myClass = [[MyClass alloc] init];</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
The <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">alloc</strong> class method returns a pointer to a newly allocated block of memory large enough to store an instance of the class. The allocated memory contains zeros except for one instance variable, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">isa</strong>, that all Objective-C objects are required to have. The <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">isa</strong> variable is automatically initialized to point to the class object that allocated the memory and enables the instance to receive messages such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">init</strong> that are used to complete initialization.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#preprocessor-directives" name="preprocessor-directives" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Preprocessor Directives</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
This section needs a lot of love, so please feel free to improve upon it!</div>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Directive</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#define</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to define constants or macros that are replaced by the compiler at runtime</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#elif</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">else if</strong> conditional statement</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#else</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">else</strong> conditional statement</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#endif</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">end if</strong> conditional statement</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#error</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to flag an error line in code</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#if</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if</strong> conditional statement</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#ifdef</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if defined</strong> conditional statement</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#ifndef</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if not defined</strong> conditional statement</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#import</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Imports a header file. This directive is identical to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">#include</strong>, except that it won’t include the same file more than once</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#include</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Includes a header file</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#pragma</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used for commenting code or inhibiting compiler warnings</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#undef</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to undefine and redefine macros</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">#warning</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to flag a warning line in code</td></tr>
</tbody></table>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#compiler-directives" name="compiler-directives" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Compiler Directives</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Also see the <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#literals" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">literals</a> section.</div>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#classes-and-protocols" name="classes-and-protocols" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Classes and Protocols</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Directive</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@class</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Declares the names of classes defined elsewhere</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@interface</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Begins the declaration of a class or category interface</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@implementation</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Begins the definition of a class or category</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@protocol</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Begins the declaration of a formal protocol</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@required</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Declares the methods following the directive as required (default)</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@optional</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Declares the methods following the directive as optional. Classes implementing this protocol can decide whether to implement an optional method or not and should first check if the method is implemented before sending it a message.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@end</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Ends the declaration/definition of a class, category, or protocol</td></tr>
</tbody></table>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#properties" name="properties" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Properties</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Directive</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@property</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Declares a property with a backing instance variable</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@synthesize</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Synthesizes a property and allows the compiler to generate setters/getters for the backing instance variable</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@dynamic</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Tells the compiler that the setter/getter methods are not implemented by the class itself but somewhere else, like the superclass</td></tr>
</tbody></table>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#errors" name="errors" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Errors</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Directive</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@throw</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Throws an exception</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@try</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Specifies a block of code to attempt</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@catch</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Specifies what to do if an exception was thrown in the <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@try</strong>block</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@finally</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Specifies code that runs whether an exception occurred or not</td></tr>
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<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#visibility-of-instance-variables" name="visibility-of-instance-variables" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Visibility of Instance Variables</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Directive</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@private</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Limits the scope of instance variables specified below it to the class that declares it</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@protected</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Limits the scope of instance variables specified below it to declaring and inheriting classes</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@public</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Removes restrictions on the scope of instance variables specified below it</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@package</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Declares the instance variables following the directive as public inside the framework that defined the class, but private outside the framework (64-bit only)</td></tr>
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The default is <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@protected</strong>, so there is no need to explicitly specify this.</div>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#others" name="others" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Others</h4>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Directive</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@selector(method)</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Returns the compiled selector that identifies a method</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@protocol(name)</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Returns the given protocol (an instance of the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Protocol</strong> class)</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@synchronized</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Encapsulates code in a mutex lock to ensure that the block of code and the locked object can only be accessed by one thread at a time</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@autoreleasepool</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Replaces (and is 6 times faster than) the NSAutoreleasePool class</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@encode(spec)</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Yields a character string that encodes the type structure of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">spec</strong></td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@compatibility_alias</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Allows you to define an alias name for an existing class.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@defs(classname)</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Yields the internal data structure of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">classname</strong>instances</td></tr>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#literals" name="literals" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Literals</h3>
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Literals are compiler directives which provide a shorthand notation for creating common objects.</div>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Syntax</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">What it does</th></tr>
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<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@”string”</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Returns an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSString</strong> object</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@28, @3.14, @YES</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Returns an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSNumber</strong> object initialized with an appropriate class constructor, depending on the type</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@[]</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Returns an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSArray</strong> object</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@{}</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Returns an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSDictionary</strong> object</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">@()</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Dynamically evaluates the boxed expression and returns the appropriate object literal based on its value</td></tr>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#nsarray-access-syntax" name="nsarray-access-syntax" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>NSArray Access Syntax</h4>
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NSArray *example = @[ @"hi", @"there", @23, @YES ];
NSLog(@"item at index 0: %@", example[0]);</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#nsdictionary-access-syntax" name="nsdictionary-access-syntax" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>NSDictionary Access Syntax</h4>
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NSDictionary *example = @{ @"hi" : @"there", @"iOS" : @"people" };
NSLog(@"hi %@", example[@"hi"]);</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#caveats" name="caveats" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Caveats</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Similar to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSString</strong> literals, collection objects made via literal arrays and dictionaries are immutable. Instead, you will have to make a mutable copy after making the immutable dictionary or array. Additionally, you cannot have static initializers like you can with <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSString</strong>.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#methods" name="methods" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Methods</h3>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#declaration-syntax" name="declaration-syntax" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Declaration Syntax</h4>
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For methods without a return type, use <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">void</strong>:</div>
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// Does not return anything or take any arguments
- (void)someMethod;</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">+</strong> precedes declarations of class methods:</div>
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// Call on a class (e.g. [MyClass someClassMethod]);
+ (void)someClassMethod;</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">-</strong> precedes declarations of class instance methods:</div>
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// Called on an instance of a class (e.g. [[NSString alloc] init]);
- (void)someClassInstanceMethod;</div>
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Method arguments are declared after colons <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">:</strong> and the method signature should describe the argument type:</div>
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// Does something with an NSObject argument
- (void)doWorkWithObject:(NSObject *)object;</div>
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Argument and return types are declared using type casting syntax:</div>
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// Returns an NSString object for the given NSObject arguments
- (NSString *)stringFromObject:(NSObject *)object andSomeOtherObject:(NSObject *)otherObject;</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#calling-methods" name="calling-methods" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Calling Methods</h4>
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Methods are called using bracket syntax: <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">[self someMethod];</strong> or <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">[self sometMethodWithObject:object];</strong></div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">self</strong> is a reference to the method’s containing class. The <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">self</strong> variable is present in all Objective-C methods and it is one of two hidden arguments passed to code that implements a method, the other being <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">_cmd</strong>, which identifies the received message.</div>
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At times, it is necessary to call a method in the superclass using <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">[super someMethod];</strong>.</div>
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Under the hood, methods are implemented via message sending and they are turned into a variation of one of these two C functions:</div>
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id objc_msgSend(id self, SEL op, ...);
id objc_msgSendSuper(struct objc_super *super, SEL op, ...);</div>
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There is a great Beginners Guide to Objective-C tutorial series that covers Calling methods in more detail. Check it out: <a href="http://ios-blog.co.uk/tutorials/objective-c-guide-for-developers-part-2/#methods" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Calling Methods in Objective-C</a>.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#testing-selectors" name="testing-selectors" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Testing Selectors</h4>
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If you’d like to test if a class responds to a certain selector before you send it (and possibly crash), you can do so with:</div>
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if ([someClassOrInstance respondsToSelector:@selector(someMethodName)])
{
    // Call the selector or do something here
}</div>
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This pattern is common when you have a delegate implemented and need to test for methods declared as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@optional</strong> before calling them on the delegate object.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#properties-and-variables" name="properties-and-variables" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Properties and Variables</h3>
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Declaring an Objective-C Property allows you to maintain a reference to an object within a class or to pass objects between classes.</div>
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Public properties are declared in the header ( <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.h</strong>) file:</div>
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@interface MyClass : NSObject

@property (readonly, nonatomic, strong) NSString *fullName;

// Class extension for private variables / properties
@interface MyClass ()
{
    // Instance variable
    int somePrivateInteger;

// Private properties
    @property (nonatomic, strong) NSString *firstName;
    @property (nonatomic, strong) NSString *lastName;
    @property (readwrite, nonatomic, strong) NSString *fullName;
}
@end

@implementation MyClass

// Class implementation goes here

// Or
@property (xxx) SomeClass *someProperty;</div>
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where <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">xxx</strong> can be a combination of:</div>
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<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Type</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">What it does</th></tr>
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<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">copy</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Creates an immutable copy of the object upon assignment and is typically used for creating an immutable version of a mutable object. Use this if you need the value of the object as it is at this moment, and you don’t want that value to reflect any future changes made by other owners of the object.</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">assign</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Generates a setter which assigns the value directly to the instance variable, rather than copying or retaining it. This is typically used for creating properties for primitive types ( <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">float</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">int</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">BOOL</strong>, etc).</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">weak</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Variables that are <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">weak</strong> can still point to objects but they do not become owners (or increase the retain count by 1). If the object’s retain count drops to 0, the object will be deallocated from memory and the weak pointer will be set to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">nil</strong>. It’s best practice to create all delegates and <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">IBOutlet</strong>‘s as weak references since you do not own them.</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">unsafe_unretained</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">An unsafe reference is similar to a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">weak</strong> reference in that it doesn’t keep its related object alive, but it won’t be set to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">nil</strong> if the object is deallocated. This can lead to crashes due to accessing that deallocated object and therefore you should use<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">weak</strong> unless the OS or class does not support it.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">strong</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">This is the default and is required when the attribute is a pointer to an object. The automatically generated setter will retain (i.e. increment the retain count of) the object and keep the object alive until released.</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">readonly</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">This only generates a getter method so it won’t allow the property to be changed via the setter method.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">readwrite</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">This is the default and generates both a setter and a getter for the property. Often times, a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">readonly</strong>property will be publicly defined and then a<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">readwrite</strong> for the same property name will be privately redefined to allow mutation of the property value within that class only.</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">atomic</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">This is the default and means that only one thread can access the property at a time (i.e. it’s thread-safe) and is typically slower in performance to use.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">nonatomic</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">This is used to allow multiple threads to access the property at a time. (i.e. it’s <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NOT</strong> thread-safe) and is typically faster in performance to use.</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">getter=method</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to specify a different name for the property’s getter method. This is typically done for boolean properties (e.g. <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">getter=isFinished</strong>)</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">setter=method</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to specify a different name for the property’s setter method. (e.g.<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">setter=setProjectAsFinished</strong>)</td></tr>
</tbody></table>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#accessing-properties" name="accessing-properties" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Accessing Properties</h4>
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Properties can be accessed using either bracket syntax or dot notation, with dot notation being cleaner to read.</div>
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[self myProperty];

// Or
self.myProperty</div>
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</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#local-variables" name="local-variables" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Local Variables</h4>
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Local variables exist only within the scope of a method.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 572px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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- (void)doWork
{
   NSString *localStringVariable = @"Some local string variable.";
   [self doSomethingWithString:localStringVariable];
}</div>
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</div>
</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#naming-conventions" name="naming-conventions" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Naming Conventions</h3>
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The general rule of thumb: Clarity and brevity are both important, but clarity should never be sacrificed for brevity.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#methods-and-properties" name="methods-and-properties" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Methods and Properties</h4>
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These both use <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">camelCase</strong> where the first letter of the first word is lowercase and the first letter of each additional word is capitalized.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#class-names-and-protocols" name="class-names-and-protocols" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Class names and Protocols</h4>
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These both use <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">CapitalCase</strong> where the first letter of every word is capitalized.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#methods-1" name="methods-1" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Methods</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
These should use verbs if they perform some action (e.g.<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">performInBackground</strong>). You should be able to infer what is happening, what arguments a method takes, or what is being returned just by reading a method signature.</div>
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Example:</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 860px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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// Correct
- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    // Code
}

// Incorrect (not expressive enough)
- (UITableViewCell *)table:(UITableView *)tableView cell:(NSIndexPath *)indexPath
{
    // Code
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#properties-and-local-variables" name="properties-and-local-variables" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Properties and Local Variables</h4>
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When using properties, instance variables are internally created with a preceeding underscore, so <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">myVariableName</strong> is created as<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">_myVariableName</strong>. However, Objective-C now synthesizes these properties for you so you should never have to access that underscored instance variable directly except in a custom setter.</div>
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Instead, instance variables should always be accessed and mutated using<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">self.</strong></div>
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Local variables should not contain underscores.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#constants-1" name="constants-1" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Constants</h4>
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These should start with <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">k</strong> and <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">XXX</strong> where <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">XXX</strong> is a prefix, possibly your initials, to avoid naming conflicts. You should not be afraid to be expressive with your constant naming, especially if it’s a global constant. Using<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">kRPNavigationFadeOutAnimationDuration</strong> is much better than<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">fadeOutTiming</strong>.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#blocks" name="blocks" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Blocks</h3>
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Blocks in Objective-C are essentially anonymous functions that are used to pass arbitrary code between methods or to execute code as a callback within a method. Since blocks are implemented as closures, the surrounding state is also captured (which can sometimes lead to retain cycles).</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#syntax" name="syntax" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Syntax</h4>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 660px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
// As a local variable
returnType (^blockName)(parameterTypes) = ^returnType(parameters) {
    // Block code here
};

// As a property
@property (nonatomic, copy) returnType (^blockName)(parameterTypes);

// As a method parameter
- (void)someMethodThatTakesABlock:(returnType (^)(parameterTypes))blockName {
    // Block code here
};

// As an argument to a method call
[someObject someMethodThatTakesABlock: ^returnType (parameters) {
    // Block code here
}];

// As a typedef
typedef returnType (^TypeName)(parameterTypes);
TypeName blockName = ^(parameters) {
    // Block code here
};</div>
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</pre>
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Check out our dedicated article for more detail about <a href="http://ios-blog.co.uk/tutorials/programming-with-blocks-an-overview/?utm_source=internalLink&utm_medium=internalLink&utm_term=internalLink&utm_content=internalLink&utm_campaign=internalLink" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Objective-C Programming with blocks</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#mutating-block-variables" name="mutating-block-variables" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Mutating block variables</h4>
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Since variables within a block are just snapshots of what they were outside of the block scope, you must preceed any variables that you want to mutate within the block with <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">__block</strong>, such as:</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
__block int someIncrementer = 0;
[someObject someMethodThatTakesABlock:^{
    someIncrementer++;
}];</div>
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</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#retain-cycles" name="retain-cycles" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Retain cycles</h4>
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Since blocks strongly capture all variables within the scope of the block, you have to be careful how you setup your blocks code. Here are two examples of retain cycles:</div>
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<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
[someObject someMethodThatTakesABlock:^{
    [someObject performSomeAction];  // Will raise a warning
}];

[self someMethodThatTakesABlock:^{
    [self performSomeAction];       // Will raise a warning
}];</div>
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</div>
</pre>
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In both of these cases, the object which performs the block owns the block, which also owns the object. This creates a loop, or a retain cycle, which means the memory is eventually leaked.</div>
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To get around this warning you can either refactor the code to be:</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 500px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
[self someMethodThatTakesABlock:^{
    [object performSomeAction];   // No retain cycle here
}];</div>
</td></tr>
</tbody></table>
</div>
</pre>
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Or you can use a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">__weak</strong> object:</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 508px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
__weak typeof(self) weakSelf = self;
[self someMethodThatTakesABlock:^{
    [weakSelf performSomeAction];  // No retain cycle here
}];</div>
</td></tr>
</tbody></table>
</div>
</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#control-statements" name="control-statements" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Control Statements</h3>
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Objective-C uses all of the same control statements that other languages have:</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#if-else-if-else" name="if-else-if-else" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>If-Else If-Else</h4>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 508px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
if (someTestCondition) {
    // Code to execute if the condition is true
} else if (someOtherTestCondition) {
    // Code to execute if the other test condition is true
} else {
    // Code to execute if the prior conditions are false
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#ternary-operators" name="ternary-operators" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Ternary Operators</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
The shorthand notation for an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if-else</strong> statement is a ternary operator of the form: <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">someTestCondition ? doIfTrue : doIfFalse;</strong></div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Example:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
- (NSString *)stringForTrueOrFalse:(BOOL)trueOrFalse
{
    return trueOrFalse ? @"True" : @"False";
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
There is also another lesser known form: <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">A ?: B;</strong> which basically returns <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">A</strong>if <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">A</strong> is <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">YES</strong> or non-nil, otherwise it returns <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">B</strong>.</div>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#for-loops" name="for-loops" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>For Loops</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
For more detail and explanation see: <a href="http://ios-blog.co.uk/tutorials/objective-c-guide-for-developers-part-1/#loops" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Objective-C: Loops</a></div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
for (int i = 0; i < totalCount; i++) {
    // Code to execute while i < totalCount
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#fast-enumeration" name="fast-enumeration" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Fast Enumeration</h4>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
for (Person *person in arrayOfPeople) {
    // Code to execute each time
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
where <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">arrayOfPeople</strong> can be any object that conforms to the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSFastEnumeration</strong> protocol. <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSArray</strong> and <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSSet</strong> enumerate over their objects, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSDictionary</strong> enumerates over keys, and<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSManagedObjectModel</strong> enumerates over entities.</div>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#while-loop" name="while-loop" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>While Loop</h4>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
while (someTextCondition) {
   // Code to execute while the condition is true
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#do-while-loop" name="do-while-loop" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Do While Loop</h4>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
do {
    // Code to execute while the condition is true
} while (someTestCondition);</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#switch" name="switch" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Switch</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Switch statements are often used in place of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">if</strong> statements if there is a need to test if a certain variable matches the value of another constant or variable. For example, you may want to test if an error code integer you received matches an existing constant value or if it’s a new error code.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
switch (errorStatusCode)
{
    case kRPNetworkErrorCode:
        // Code to execute if it matches
        break;

case kRPWifiErrorCode:
        // Code to execute if it matches
        break;

default:
        // Code to execute if nothing else matched
        break;
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#exiting-loops" name="exiting-loops" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Exiting Loops</h4>
<ul class="disc" style="background-color: white; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; list-style-image: initial; list-style-position: outside; margin: 0px 0px 20px 30px; padding: 0px; vertical-align: baseline;">
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">return</strong> : Stops execution and returns to the calling function. It can also be used to return a value from a method.</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;"><strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">break</strong> : Used to stop execution of a loop.</li>
</ul>
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Newer enumeration methods now have special <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">BOOL</strong> variables (e.g. <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">BOOL *stop</strong>) that are used to stop loop execution. Setting that variable to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">YES</strong>within the loop is similar to calling <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">break</strong>.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#enumeration" name="enumeration" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Enumeration</h3>
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Fast enumeration was already mentioned in the <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#control-statements" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">control statements</a> section, but many collection classes also have their own block-based methods for enumerating over a collection.</div>
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Block-based methods perform almost as well as using fast enumeration, but they just provide extra options for enumerating over collections. An example of block-based enumeration over an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSArray</strong> would be:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
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NSArray *people = @[ @"Bob", @"Joe", @"Penelope", @"Jane" ];
[people enumerateObjectsUsingBlock:^(NSString *nameOfPerson, NSUInteger idx, BOOL *stop) {
    NSLog(@"Person's name is: %@", nameOfPerson);
}];</div>
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</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#extending-classes" name="extending-classes" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Extending Classes</h3>
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There are a few different ways to extend a class in Objective-C, with some approaches being much easier than others.</div>
<table style="background-color: white; border-collapse: collapse; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 479px;"><thead style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Approach</th><th align="center" style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Difficulty</th><th style="background-color: #333333; border: 1px solid rgb(204, 204, 204); color: white; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Purpose</th></tr>
</thead><tbody style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#inheritance" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Inheritance</a></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Easy</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used if all you want to do is inherit behavior from another class, such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSObject</strong></td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#categories" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Category</a></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Easy</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used if all you need to do is add additional methods to that class. If you also need to add instance variables to an existing class using a category, you can fake this by using associative references.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#delegation" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Delegation</a></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Easy</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used to allow one class to react to changes in or influence behavior of another class while minimizing coupling.</td></tr>
<tr style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#subclassing" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Subclass</a></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Can be difficult</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Used if you need to add methods and properties to an existing class or if you want to inherit behavior from an existing class. Some classes are not designed to be subclassed.</td></tr>
<tr style="background-color: #eeeeee; background-position: initial initial; background-repeat: initial initial; border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 0px; vertical-align: baseline;"><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;"><a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#swizzling" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Swizzle</a></td><td align="center" style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Can be difficult</td><td style="border: 1px solid rgb(204, 204, 204); font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; padding: 6px; vertical-align: baseline;">Swizzling allows you to replace a method in an existing class with one of your own making. This approach can lead to a lot of unexpected behavior, so it should be used very sparingly.</td></tr>
</tbody></table>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#inheritance" name="inheritance" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Inheritance</h3>
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Inheritance essentially allows you to create concrete <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#subclassing" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">subclasses</a>, which typically have specialized behavior, while inheriting all methods and properties from a superclass which are specified as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@public</strong> or<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@protected</strong> within the superclass’ header file.</div>
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Looking through any framework or open source project, you can see the use of inheritance to not only get behavior for free, but to also consolidate code and allow it to be easily reused. Examples of this approach can be seen with any of the mutable framework classes such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSMutableString</strong>which is a subclass of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSString</strong>.</div>
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In Objective-C, all objects have much of their behavior defined by the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSObject</strong> class through the act of class inheritance. Without inheritance, you would have to implement common methods like object or class equality checks on your own and you’d end up with a lot of duplicate code across classes.</div>
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// MyClass inherits all behavior from the NSObject class
@interface MyClass : NSObject

// Class implementation

- (UIImage *)croppedImageWithSize:(CGSize)size;
- (UIImage *)resizedImageWithSize:(CGSize)size;

@implementation UIImage (ResizeCrop)

- (UIImage *)croppedImageWithSize:(CGSize)size
{
    // Implementation code here
}

- (UIImage *)resizedImageWithSize:(CGSize)size
{
    // Implementation code here
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
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You could then call these methods on any instances of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIImage</strong> or it’s subclasses such as:</div>
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UIImage *croppedImage = [userPhoto croppedImageWithSize:photoSize];</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#associative-references" name="associative-references" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Associative References</h4>
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Unless you have access to the source code for a class at compile time, it is not possible to add instance variables and properties to a class by using a category. Instead, you have to essentially fake this by using a feature of the Objective-C runtime called <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">associative references</strong>.</div>
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For example, let’s say that we want to add a public property to the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIScrollView</strong> class to store a reference to a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIView</strong> object, but we don’t have access to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIScrollView</strong>‘s source code. We would have to create a category on <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIScrollView</strong> and then create a pair of getter/setter methods for this new property to store a reference like this:</div>
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UIScrollView+UIViewAdditions.h</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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#import <UIKit/UIKit.h>

@interface UIScrollView (UIViewAdditions)

@property (nonatomic, strong) UIView *myCustomView;

static char UIScrollViewMyCustomView;

@implementation UIScrollView (UIViewAdditions)

@dynamic myCustomView;

- (void)setMyCustomView:(UIView *)customView
{
    [self willChangeValueForKey:@"myCustomView"];
    objc_setAssociatedObject(self, &UIScrollViewMyCustomView, customView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    [self didChangeValueForKey:@"myCustomView"];
}

- (UIView *)myCustomView {
    return objc_getAssociatedObject(self, &UIScrollViewMyCustomView);
}

@end</div>
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Let’s explain a bit about what’s happening here:</div>
<ul class="disc" style="background-color: white; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; list-style-image: initial; list-style-position: outside; margin: 0px 0px 20px 30px; padding: 0px; vertical-align: baseline;">
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">We create a static key called <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIScrollViewMyCustomView</strong> that we can use to get and set the associated object. Declaring it as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">static</strong>ensures that it is unique since it always points to the same memory address.</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Next, we declare the property we are adding as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@dynamic</strong> which tells the compiler that the getter/setter is not implemented by the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIScrollView</strong> class itself.</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Within the setter, we use <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">willChangeValueForKey</strong> followed by<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">didChangeValueForKey</strong> to ensure that we notify any key-value observers of a change to this property.</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Within the setter, we use <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">objc_setAssociatedObject</strong> to store a reference to the object that we really care about, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">customView</strong> under the static key that we created. <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">&</strong> is used to denote that it is a pointer to a pointer to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UIScrollViewMyCustomView</strong></li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Within the getter, we retrieve the object reference using<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">objc_getAssociatedObject</strong> and a pointer to the static key</li>
</ul>
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We could then use the property just like we would any other property:</div>
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UIScrollView *scrollView = [[UIScrollView alloc] init];
scrollView.myCustomView = [[UIView alloc] init];
NSLog(@"Custom view is %@", scrollView.myCustomView);
// Custom view is <UIView: 0x8e4dfb0; frame = (0 0; 0 0); layer = <CALayer: 0x8e4e010>></div>
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More info from the docs:</div>
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The [objc_setAssociatedObject] function takes four parameters: the source object, a key, the value, and an association policy constant. The key is a void pointer.</div>
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The key for each association must be unique. A typical pattern is to use a static variable. The policy specifies whether the associated object is assigned, retained, or copied, and whether the association is be made atomically or non-atomically. This pattern is similar to that of the attributes of a declared property</div>
</blockquote>
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The possible property declaration attributes are:</div>
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OBJC_ASSOCIATION_RETAIN_NONATOMIC, OBJC_ASSOCIATION_ASSIGN, OBJC_ASSOCIATION_COPY_NONATOMIC, OBJC_ASSOCIATION_RETAIN, OBJC_ASSOCIATION_COPY</div>
</blockquote>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#class-extension-categories" name="class-extension-categories" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Class Extension Categories</h4>
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In the section about <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#declaring-classes" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">declaring classes</a>, it shows how the private instance variables and properties within a class are actually added to the class by using an anonymous (unnamed) category, also known as a class extension.</div>
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// Class extensions for private variables / properties
@interface MyClass ()
{
    int somePrivateInt;

// Re-declare as a private read-write version of the public read-only property
    @property (readwrite, nonatomic, strong) SomeClass *someProperty;
}
@end</div>
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Class extensions are the only way that you can add variables and properties using a category, so you must have access to the source code at compile time in order to use this method.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#core-data-categories" name="core-data-categories" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Core Data Categories</h4>
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Categories are very useful when you are working with Core Data models and want to add additional methods to an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSManagedObject</strong> subclass without worrying about Xcode writing over the model class each time you migrate a model.</div>
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Model classes should be kept to a minimum, containing only the model properties and Core Data generated accessor methods. All others, such as transient methods, should be implemented in a category on the model class.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#naming-conflicts" name="naming-conflicts" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Naming Conflicts</h4>
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Great advice from <a href="https://developer.apple.com/library/ios/documentation/cocoa/conceptual/ProgrammingWithObjectiveC/CustomizingExistingClasses/CustomizingExistingClasses.html" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">Apple's docs</a> :</div>
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Because the methods declared in a category are added to an existing class, you need to be very careful about method names.</div>
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If the name of a method declared in a category is the same as a method in the original class, or a method in another category on the same class (or even a superclass), the behavior is undefined as to which method implementation is used at runtime. This is less likely to be an issue if you’re using categories with your own classes, but can cause problems when using categories to add methods to standard Cocoa or Cocoa Touch classes.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#delegation" name="delegation" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Delegation</h3>
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Objective-C Delegation is basically a way to allow one class to react to changes made in another class or to influence the behavior of another class while minimizing coupling between the two.</div>
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The most commonly known example of the delegate pattern in iOS is with<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITableViewDelegate</strong> and <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITableViewDataSource</strong>. When you tell the compiler that your class conforms to these protocols, you are essentially agreeing to implement certain methods within your class that are required for a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITableView</strong> to properly function.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#conforming-to-an-existing-protocol" name="conforming-to-an-existing-protocol" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Conforming to an Existing Protocol</h4>
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To conform to an existing protocol, import the header file that contains the protocol declaration (not necessary for framework classes). Then, insert the protocol name within <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">< ></strong> symbols and separate multiple protocols by a comma. Both options shown below will work just fine, but I prefer to keep them in the header file since it feels cleaner to me.</div>
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<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Option 1</strong>: In your <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.h</strong> file:</div>
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#import "RPLocationManager.h"

@interface MyViewController : UIViewController <RPLocationManagerDelegate, UITableViewDelegate, UITableViewDataSource>

@interface MyViewController () <RPLocationManagerDelegate, UITableViewDelegate, UITableViewDataSource>
{
    // Class extension implementation
}
@end</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#creating-your-own-protocol" name="creating-your-own-protocol" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Creating Your Own Protocol</h4>
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To create your own protocol for other classes to conform to, follow this syntax:</div>
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RPLocationManager.h</div>
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#import <SomeFrameworksYouNeed.h>

// Declare your protocol and decide which methods are required/optional
// for the delegate class to implement
@protocol RPLocationManagerDelegate <NSObject>
- (void)didAcquireLocation:(CLLocation *)location;
- (void)didFailToAcquireLocationWithError:(NSError *)error;
@optional
- (void)didFindLocationName:(NSString *)locationName;
@end

@interface RPLocationManager : NSObject

// Create a weak, anonymous object to store a reference to the delegate class
@property (nonatomic, weak) id <RPLocationManagerDelegate>delegate;

// Implement any other methods here

// When ready, notify the delegate method
    [self.delegate didAcquireLocation:locationObject];
}</div>
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Optional Methods</div>
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- (void)reverseGeoCode
{
    // Perform some work

// When ready, notify the delegate method
    if ([self.delegate respondsToSelector:@selector(didFindLocationName:)]) {
        [self.delegate didFindLocationName:locationName];
    }
}</div>
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The only difference between <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@required</strong> and <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">@optional</strong> methods is that you should always check if the referenced <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">delegate</strong> implemented an optional method before calling it on that class.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#implementing-delegate-methods" name="implementing-delegate-methods" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Implementing Delegate Methods</h4>
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To implement a delegate method, just conform to the protocol like was discussed earlier, and then write it as if it was a normal method:</div>
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MyViewController.m</div>
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- (void)didFindLocationName:(NSString *)locationName
{
    NSLog(@"We found a location with the name %@", locationName);
}</div>
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</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#subclassing" name="subclassing" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Subclassing</h3>
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Subclassing is essentially the same as <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#inheritance" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">inheritance</a>, but you would typically create the subclass to either</div>
<ul class="disc" style="background-color: white; border: 0px; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 21px; list-style-image: initial; list-style-position: outside; margin: 0px 0px 20px 30px; padding: 0px; vertical-align: baseline;">
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Override a method or property implementation in the superclass; or</li>
<li style="border: 0px; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: 18px; margin: 0px 0px 12px; padding: 0px; vertical-align: baseline;">Create specialized behavior for the subclass (e.g. <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Toyota</strong> is a subclass of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Car</strong>… it still has tires, an engine, etc, but it has additional custom behavior that uniquely makes it a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Toyota</strong>)</li>
</ul>
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Many design patterns, such as <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#categories" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">categories</a> and <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#delegation" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">delegation</a>, exist so that you don’t have to subclass another class. For example, the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITableViewDelegate</strong> protocol was created to allow you to provide the implementation of methods like <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">tableView:didSelectRowAtIndexPath:</strong> in your own class instead of having to subclass <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITableView</strong> to override that method.</div>
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Other times, classes like <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSManagedObject</strong> are designed to be easily subclassed. The general rule of thumb is to subclass another class only if you can satisfy the <a href="http://en.wikipedia.org/wiki/Liskov_substitution_principle" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">Liskov substitution principle</a> :</div>
<blockquote style="background-color: white; border-left-color: rgb(107, 196, 234); border-left-style: solid; border-width: 0px 0px 0px 4px; color: #6bc4ea; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 17px; font-style: italic; line-height: 24px; margin: 0px 0px 20px; padding: 0px 20px 0px 19px; quotes: none; vertical-align: baseline;">
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If S is a subtype of T, then objects of type T in a program may be replaced with objects of type S without altering any of the desirable properties of that program.</div>
</blockquote>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#example" name="example" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Example</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Let’s assume that we want to model cars. All cars have similar behavior and characteristics, so let’s put some of that in a superclass called <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Car</strong>.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Car.h</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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#import <Foundation/Foundation.h>

@interface Car : NSObject

@property (nonatomic, strong) NSString *make;
@property (nonatomic, strong) NSString *model;
@property (nonatomic, assign) NSInteger year;

- (void)startEngine;
- (void)pressGasPedal;
- (void)pressBrakePedal;

@implementation Car

- (void)startEngine
{
   NSLog(@"Starting the engine.");
}

- (void)pressGasPedal
{
    NSLog(@"Accelerating...");
}

- (void)pressBrakePedal
{
    NSLog(@"Decelerating...");
}

@interface Toyota : Car

- (void)preventAccident;

@implementation Toyota

- (void)startEngine
{
    // Perform custom start sequence, different from the superclass

NSLog(@"Starting the engine.");
}

- (void)preventAccident
{
    [self pressBrakePedal];

[self deployAirbags];
}

- (void)deployAirbags
{
   NSLog(@"Deploying the airbags.");
}

// Provide a sensible default for other initializers
- (instancetype)init
{
    return [self initWithFullName:@"Default User"];
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
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If you’d rather someone not use a default initializer for some rare case, you should throw an exception and provide them with an alternative solution:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 1700px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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- (instancetype)init {
        [NSException raise:NSInvalidArgumentException
                format:@"%s Using the %@ initializer directly is not supported. Use %@ instead.", __PRETTY_FUNCTION__, NSStringFromSelector(@selector(init)), NSStringFromSelector(@selector(initWithFrame:))];
    return nil;
}</div>
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</pre>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#overriding-methods" name="overriding-methods" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Overriding Methods</h4>
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If you’re subclassing another class to override a method within that class, you must be a little cautious. If you want to maintain the same behavior as the superclass, but just modify it slightly, you can call <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">super</strong> within the override like this:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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- (void)myMethod
{
    [super myMethod];

// Provide your additional custom behavior here
}</div>
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</tbody></table>
</div>
</pre>
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If you don’t want any of the superclass’s behavior for the overridden method, simply leave out that call to <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">super</strong>, but be careful that there aren’t any memory or object lifecycle consequences for doing so.</div>
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Additionally, if the superclass has primitive methods upon which other derived methods are implemented, you must ensure that you override all necessary primitive methods necessary for the derived methods to work properly.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#caveats-1" name="caveats-1" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Caveats</h4>
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Certain classes don’t lend themselves well to being easily subclassed and therefore subclassing is discouraged in those cases. An example of this is when trying to subclass a class cluster such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSString</strong> or <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSNumber</strong>. Class clusters have quite a few private classes within them so it’s difficult to ensure that you have overridden all of the primitive methods and designated initializers within the class cluster properly.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#swizzling" name="swizzling" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Swizzling</h3>
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As is often the case, clarity is better than cleverness. As a general rule, it’s typically better to work around a bug in a method implementation than it is to replace the method by using method swizzling. The reason being that other people using your code might not realize that you replaced the method implementation and then they are stuck wondering why a method isn’t responding with the default behavior.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
For this reason, we don’t discuss swizzling here but you are welcome to <a href="http://www.mikeash.com/pyblog/friday-qa-2010-01-29-method-replacement-for-fun-and-profit.html" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;" target="_blank">read up on it here</a> .</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#error-handling" name="error-handling" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Error Handling</h3>
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Errors are typically handled three different ways: assertions, exceptions, and recoverable errors. In the case of assertions and exceptions, they should only be used in rare cases since crashing your app is obviously not a great user experience.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#assertions" name="assertions" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Assertions</h3>
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Assertions are used when you want to ensure that a value is what it is supposed to be. If it’s not the correct value, you force exit the app.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 684px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
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NSAssert(someCondition, @"The condition was false, so we are exiting the app.");</div>
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Important: Do not call functions with side effects in the condition parameter of this macro. The condition parameter is not evaluated when assertions are disabled, so if you call functions with side effects, those functions may never get called when you build the project in a non-debug configuration.</div>
</blockquote>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#exceptions" name="exceptions" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Exceptions</h3>
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Exceptions are only used for programming or unexpected runtime errors. Examples: attempting to access the 6th element of an array with 5 elements (out-of-bounds access), attempting to mutate immutable objects, or sending an invalid message to an object. You usually take care of these sorts of errors with exceptions when an application is being created rather than at runtime.</div>
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An example of this might be if you have a library which requires an API key to use.</div>
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<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 1084px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
// Check for an empty API key
- (void)checkForAPIKey
{
    if (!self.apiKey || !self.apiKey.length) {
        [NSException raise:@"Forecastr" format:@"Your Forecast.io API key must be populated before you can access the API.", nil];
    }
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#try-catch" name="try-catch" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Try-Catch</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
If you’re worried that a block of code is going to throw an exception, you can wrap it in a try-catch block but keep in mind that this has slight performance implications</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 660px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
@try {
    // The code to try here
}
@catch (NSException *exception) {
    // Handle the caught exception
}
@finally {
    // Execute code here that would run after both the @try and @catch blocks
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#recoverable-errors" name="recoverable-errors" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Recoverable Errors</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Many times, methods will return an <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSError</strong> object in a failure block or as a pointer to a pointer (in the case of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSFileManager</strong>). These are typically returned for recoverable errors and offer a much more pleasant user experience since they can clue the user into what just went wrong.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 668px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
[forecastr getForecastForLocation:location success:^(id JSON) {
    NSLog(@"JSON response was: %@", JSON);
} failure:^(NSError *error, id response) {
    NSLog(@"Error while retrieving forecast: %@", error.localizedDescription);
}];</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#creating-your-own-errors" name="creating-your-own-errors" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Creating Your Own Errors</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
It’s also possible to create your own <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSError</strong> objects to return in methods.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 828px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
// Error domain & enums
NSString *const kFCErrorDomain = @"com.forecastr.errors";
typedef NS_ENUM(NSInteger, ForecastErrorType) {
    kFCCachedItemNotFound,
    kFCCacheNotEnabled
};

@implementation Forecastr

- (void)checkForecastCacheForURLString:(NSString *)urlString
                               success:(void (^)(id cachedForecast))success
                               failure:(void (^)(NSError *error))failure
{
    // Check cache for a forecast
    id cachedItem = [forecastCache objectForKey:urlString];
    if (cachedItem) {
        success(cachedItem);
    } else {
        // Return an error since it wasn't found
        failure([NSError errorWithDomain:kFCErrorDomain code:kFCCachedItemNotFound userInfo:nil]);
    }
}

@protocol AddPersonTableViewControllerDelegate <NSObject>
- (void)didSelectPerson:(Person *)person;
@end

@interface AddPersonTableViewController : UITableViewController

@property (nonatomic, weak) id <AddPersonTableViewControllerDelegate>delegate;

- (void)tableView:(UITableView *)tableView didSelectRowAtIndexPath:(NSIndexPath *)indexPath
{
    Person *person = [people objectAtIndex:indexPath.row];
    [self.delegate didSelectPerson:person];
}</div>
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</tbody></table>
</div>
</pre>
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GroupViewController.m (the normal view)</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 620px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
// Other implementation details left out, such as showing the modal view
// and setting the delegate to self

#pragma mark - AddPersonTableViewControllerDelegate

- (void)didSelectPerson:(Person *)person
{
    [self dismissViewControllerAnimated:YES completion:nil];

NSLog(@"Selected person: %@", person.fullName);
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
We left out a few implementation details, such as conforming to the<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">AddPersonTableViewControllerDelegate</strong>, but you are welcome to read the <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#delegation" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">delegation</a> section for those.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Also, notice that we dismiss the modal view controller (<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">AddPersonViewController</strong>) in the same class that originally showed it. This is the recommended approach by Apple.</div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#nsnotificationcenter" name="nsnotificationcenter" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>NSNotificationCenter</h3>
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Notifications are broadcast messages that are used to decouple classes and establish anonymous communication between objects at runtime. Notifications may be posted by any number of objects and received by any number of objects thus enabling one-to-many and many-to-many relationships between objects.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">Note</strong>: Notifications are sent synchronously so if your observer method takes a long time to return, you are essentially prevently the notification from being sent to other observing objects.</div>
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<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#registering-observers" name="registering-observers" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Registering Observers</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
You can register to be notified when a certain event has happened, including system notifications, such as a <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITextField</strong> which has begun editing.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 892px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(textFieldDidBeginEditing:)
                                             name:UITextFieldTextDidBeginEditingNotification object:self];</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
When the <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">UITextFieldTextDidBeginEditingNotification</strong> notification is broadcast by the OS framework, the <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">textFieldDidBeginEditing:</strong> will be called by <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSNotificationCenter</strong> and an object will be sent along with the notification that could contain data.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
A possible implementation of the <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">textFieldDidBeginEditing:</strong> method could be:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 740px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
#pragma mark - Text Field Observers

- (void)textFieldDidBeginEditing:(NSNotification *)notification
{
    // Optional check to make sure the method was called from the notification
    if ([notification.name isEqualToString:UITextFieldTextDidBeginEditingNotification])
    {
        // Do something
    }
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#removing-observers" name="removing-observers" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Removing Observers</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
It’s important to remove yourself as an observer when the class is deallocated, otherwise <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSNotificationCenter</strong> will attempt to call a method on a deallocated class and a crash will ensue.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 548px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
- (void)dealloc
{
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h4 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 21px; font-weight: normal; line-height: 30px; margin: 0px 0px 4px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#posting-notifications" name="posting-notifications" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Posting Notifications</h4>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
You can also create and post your own notifications. It’s best practice to keep notification names in a <a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#constants" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">constants</a> file so that you don’t accidentally misspell one of the notification names and sit there trying to figure out why the notification wasn’t sent/received.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Naming notifications:</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Notifications are identified by <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSString</strong> objects whose names are composed in this way:</div>
<blockquote style="background-color: white; border-left-color: rgb(107, 196, 234); border-left-style: solid; border-width: 0px 0px 0px 4px; color: #6bc4ea; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 17px; font-style: italic; line-height: 24px; margin: 0px 0px 20px; padding: 0px 20px 0px 19px; quotes: none; vertical-align: baseline;">
<div style="border: 0px; clear: left; font-family: inherit; font-variant: inherit; font-weight: inherit; line-height: 34px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
[Name of associated class] + [Did | Will] + [UniquePartOfName] + Notification</div>
</blockquote>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Declare a string constant, using the notification name as the string’s value:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 876px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
// Remember to put the extern of this in the header file
NSString *const kRPAppDidResumeFromBackgroundNotification = @"RPAppDidResumeFromBackgroundNotification";</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Post notification:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 956px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
[[NSNotificationCenter defaultCenter] postNotificationName:kRPAppDidResumeFromBackgroundNotification object:self];</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#view-controller-properties" name="view-controller-properties" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>View Controller Properties</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
When you are preparing to display a new view controller, you can assign data to one of it’s properties prior to display:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 540px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
MyViewController *myVC = [[MyViewController alloc] init];
myVC.someProperty = self.someProperty;
[self presentViewController:myVC animated:YES completion:nil];</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#storyboard-segue" name="storyboard-segue" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Storyboard Segue</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
When you are transitioning from one view controller to another in a storyboard, there is an easy way to pass data between the two by implementing the <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">prepareForSegue:sender:</strong> method:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 644px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
#pragma mark - Segue Handler

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
    if ([segue.identifier isEqualToString:@"showLocationSearch"] {
        [segue.destinationViewController setDelegate:self];
    } else if ([segue.identifier isEqualToString:@"showDetailView"]) {
        DetailViewController *detailView = segue.destinationViewController;
        detailView.location = self.location;
    }
}</div>
</td></tr>
</tbody></table>
</div>
</pre>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#user-defaults" name="user-defaults" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>User Defaults</h3>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
User defaults are basically a way of storing simple preference values which can be saved and restored across app launches. It is not meant to be used as a data storage layer, like Core Data or sqlite.</div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#storing-values" name="storing-values" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Storing Values</h3>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 596px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
[userDefaults setValue:@"Some value" forKey:@"RPSomeUserPreference"];
[userDefaults synchronize];</div>
</td></tr>
</tbody></table>
</div>
</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
Always remember to call <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">synchronize</strong> on the defaults instance to ensure they are saved properly.</div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#retrieving-values" name="retrieving-values" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Retrieving Values</h3>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 596px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
NSUserDefaults *userDefaults = [NSUserDefaults standardUserDefaults];
id someValue = [userDefaults valueForKey:@"RPSomeUserPreference"];</div>
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</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
There are also other convenience methods on <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">NSUserDefaults</strong> instances such as <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">boolForKey:</strong>, <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">stringForKey:</strong>, etc.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#top-of-article" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;">Back to top</a></div>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#common-patterns" name="common-patterns" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Common Patterns</h3>
<h3 style="background-color: white; border: 0px; color: #181818; font-family: MelbourneRegular, 'Helvetica Nueue', Arial, sans-serif; font-size: 28px; font-weight: normal; line-height: 34px; margin: 0px 0px 8px; padding: 0px; vertical-align: baseline;">
<a href="http://ios-blog.co.uk/resources/objective-c-cheat-sheet/#singletons" name="singletons" style="border: 0px; color: #6bc4ea; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; font-weight: inherit; line-height: inherit; margin: 0px; outline: 0px; padding: 0px; vertical-align: baseline;"></a>Singletons</h3>
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Singleton’s are a special kind of class where only one instance of the class exists for the current process. They are a convenient way to share data between different parts of an app without creating global variables or having to pass the data around manually, but they should be used sparingly since they often create tighter coupling between classes.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
To turn a class into a singleton, you place the following method into the implementation ( <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">.m</strong>) file, where the method name is prefixed with <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">shared</strong>plus another word which best describes your class. For example, if the class is a network or location manager, you would name the method<strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">sharedManager</strong> instead of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">sharedInstance</strong>.</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 460px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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+ (instancetype)sharedInstance
{
   static id sharedInstance = nil;
   static dispatch_once_t onceToken;
   dispatch_once(&onceToken, ^{
      sharedInstance = [[self alloc] init];
   });

return sharedInstance;
}</div>
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</pre>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
The use of <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">dispatch_once</strong> ensures that this method is only ever executed once, even if it’s called multiple times across many classes or different threads.</div>
<div style="background-color: white; border: 0px; clear: left; color: #444444; font-family: HelveticaNeue, 'Helvetica Neue', Helvetica, Arial, sans-serif; font-size: 14px; line-height: 28px; margin-bottom: 20px; max-width: 480px; padding: 0px; vertical-align: baseline; word-wrap: break-word;">
If the above code were placed within <strong style="background-color: #f1f1f1; border: 0px; color: #333333; font-family: inherit; font-size: inherit; font-style: inherit; font-variant: inherit; line-height: inherit; margin: 0px; padding: 2px; vertical-align: baseline;">MyClass</strong>, then you would get a reference to that singleton class in another class with the following code:</div>
<pre style="background-color: white; border: 0px; color: #444444; font-family: inherit; font-size: 14px; line-height: 21px; margin-left: -20px; padding: 0px; vertical-align: baseline;"><div class="codecolorer-container text default" style="background-color: #f1f1f1; border: 1px solid rgb(159, 159, 159); color: black; font-family: Monaco, 'Lucida Console', monospace; font-size: 13px; line-height: 1.4em; margin: 0px 0px 10px 20px; overflow: auto; padding: 0px; vertical-align: baseline; white-space: nowrap; width: 435px;">
<table cellpadding="0" cellspacing="0" style="border-collapse: collapse; border: 0px; font-size: 13px; line-height: 1.4em; margin: 20px 0px; padding: 0px; vertical-align: baseline; width: 468px;"><tbody style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;">
<tr style="background-color: #eeeeee; border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><td class="line-numbers" style="border-right-color: rgb(159, 159, 159); border-right-style: solid; border-width: 0px 1px 0px 0px; color: #888888; line-height: 1.4em; margin: 0px; padding: 5px; text-align: right; vertical-align: baseline;"><div style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline; width: 23px;">
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</td><td style="border: 0px; line-height: 1.4em; margin: 0px; padding: 0px; vertical-align: baseline;"><div class="text codecolorer" style="background-color: #f1f1f1; border: 0px; line-height: 1.4em; margin: 0px; padding: 5px; vertical-align: baseline;">
MyClass *myClass = [MyClass sharedInstance];
[myClass doSomething];
NSLog(@"Property value is %@", myClass.someProperty);</div>
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</tbody></table>
</div>
</pre>

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