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POHow to handle Objective-C protocols that contain properties?
 

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  1. POHow to handle Objective-C protocols that contain properties?
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    <p>I've seen usage of Objective-C protocols get used in a fashion such as the following:</p> <pre><code>@protocol MyProtocol &lt;NSObject&gt; @required @property (readonly) NSString *title; @optional - (void) someMethod; @end </code></pre> <p>I've seen this format used instead of writing a concrete superclass that subclasses extend. The question is, if you conform to this protocol, do you need to synthesize the properties yourself? If you're extending a superclass, the answer is obviously no, you do not need to. But how does one deal with properties that a protocol requires to conform to?</p> <p>To my understanding, you still need to declare the instance variables in the header file of an object that conforms to a protocol that requires these properties. In that case, can we assume that they're just a guiding principle? CLearly the same isn't the case for a required method. The compiler will slap your wrist for excluding a required method that a protocol lists. What's the story behind properties though?</p> <p>Here's an example that generates a compile error (Note: I've trimmed the code which doesn't reflect upon the problem at hand):</p> <p>MyProtocol.h</p> <pre><code>@protocol MyProtocol &lt;NSObject&gt; @required @property (nonatomic, retain) id anObject; @optional </code></pre> <p>TestProtocolsViewController.h</p> <pre><code>- (void)iDoCoolStuff; @end #import &lt;MyProtocol.h&gt; @interface TestProtocolsViewController : UIViewController &lt;MyProtocol&gt; { } @end </code></pre> <p>TestProtocolsViewController.m</p> <pre><code>#import "TestProtocolsViewController.h" @implementation TestProtocolsViewController @synthesize anObject; // anObject doesn't exist, even though we conform to MyProtocol. - (void)dealloc { [anObject release]; //anObject doesn't exist, even though we conform to MyProtocol. [super dealloc]; } @end </code></pre>
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