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    <p>Here, you're declaring an instance variable named <code>aVar</code>:</p> <pre><code>@interface myclass : UIImageView { int aVar; } </code></pre> <p>You can now use this variable within your class:</p> <pre><code>aVar = 42; NSLog(@"The Answer is %i.", aVar); </code></pre> <p>However, instance variables are private in Objective-C. What if you need other classes to be able to access and/or change <code>aVar</code>? Since methods are public in Objective-C, the answer is to write an accessor (getter) method that returns <code>aVar</code> and a mutator (setter) method that sets <code>aVar</code>:</p> <pre><code>// In header (.h) file - (int)aVar; - (void)setAVar:(int)newAVar; // In implementation (.m) file - (int)aVar { return aVar; } - (void)setAVar:(int)newAVar { if (aVar != newAVar) { aVar = newAVar; } } </code></pre> <p>Now other classes can get and set <code>aVar</code> via:</p> <pre><code>[myclass aVar]; [myclass setAVar:24]; </code></pre> <p>Writing these accessor and mutator methods can get quite tedious, so in Objective-C 2.0, Apple simplified it for us. We can now write:</p> <pre><code>// In header (.h) file @property (nonatomic, assign) int aVar; // In implementation (.m) file @synthesize aVar; </code></pre> <p>...and the accessor/mutator methods will be automatically generated for us.</p> <p><strong>To sum up:</strong></p> <ul> <li><p><code>int aVar;</code> declares an instance variable <code>aVar</code></p></li> <li><p><code>@property (nonatomic, assign) int aVar;</code> declares the accessor and mutator methods for <code>aVar</code></p></li> <li><p><code>@synthesize aVar;</code> implements the accessor and mutator methods for <code>aVar</code></p></li> </ul>
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    1. COgreat explanation (though Rob and chpwn are also very clear), thankyou all.
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    2. CO@Nigel: Glad to be of assistance! :)
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    3. CONote that with the iPhone OS and 64 bit Mac OS X, the environment variable declaration is optional.
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