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POWarning: MyClass:NSObject does not implement key value observing? How can that be?
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  1. POWarning: MyClass:NSObject does not implement key value observing? How can that be?
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    copied!<p>I just recently resumed work on a Cocoa project that I left a few months ago. Cocoa is a strange beast if you have not been using it for a while.</p> <p>Anyway, at some point the compiler started dropping warnings:</p> <blockquote> <p>Incomplete implementation of class 'MyClass'<br> Method definition for '-addObserver:forKeyPath:options:context' not found<br> Method definition for '-removeObserver:forKeyPath:' not found<br> Class 'MyClass' does not fully implement the 'MyZoomScrollViewDataSource' protocol </p> </blockquote> <p>But <code>MyClass</code> is derived from <code>NSObject</code>, which does in fact implement <code>-addObserver:forKeyPath:</code> and <code>-removeObserver:forKeyPath:context:</code>.</p> <p>The protocol looks like this:</p> <pre><code>@protocol MyZoomScrollViewDataSource // The range of Data that should be shown. This corresponds to the horizontal // zoom and the scroll value of self. @property FRange selectionRange; // Also, make sure the dataSource is KVO compliant - (void)addObserver:(NSObject *)anObserver forKeyPath:(NSString *)keyPath options:(NSKeyValueObservingOptions)options context:(void *)context; - (void)removeObserver:(NSObject *)anObserver forKeyPath:(NSString *)keyPath; @end </code></pre> <p>The class looks like this:</p> <pre><code>@interface MyClass : NSObject &lt;MyZoomScrollViewDataSource&gt; { IBOutlet Outlets... variables... } @properties... (IBAction)actions... - methods... @end </code></pre> <p>I guess my Cocoa skills are in deep need for a refresh. But still, these methods should be inherited from <code>NSObject</code>, so how can <code>MyClass</code> not implement these methods?</p>
 

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