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7210537
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2011-08-26T21:02:38.240
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2011-08-26T21:07:47.290
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2011-08-26T21:07:47.290
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4
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Defining such a category on all such classes in general is not easily solvable. But your actual problem seems simpler: How does one add a category method to <code>NSManagedObject</code> for use only with subclasses that implement <code><SOManagedObject></code>? This is solvable. What you want to do is add the method to <code>NSManagedObject</code>, then check that the instance you're working with can handle the messages you want to send it from <code><SOManagedObject></code>. Let us suppose that we are given: <pre><code>/* SOManagedObject.h */ @protocol SOManagedObject - (void)frobble_so; - (void)bobble_so; @end </code></pre> Now let's add a category method to all <code>NSManagedObject</code> subclasses that implement <code>SOManagedObject</code>: <pre><code>/* NSManagedObject+SOConvenience.h */ @interface NSManagedObject (SOConvience) /* Frobbles and bobbles - no effect on non-<SOManagedObject>-conforming * instances. */ - (void)frobbleAndBobble_so; @end </code></pre> To do so, we implement the method like so: <pre><code>/* NSManagedObject+SOConvenience.m */ @implementation NSManagedObject (SOConvenience) - (void)frobbleAndBobble_so { if (![self conformsToProtocol:@protocol(SOManagedObject)]) return; NSLog(@"%s: Thunderbirds are GO! Let's frobble and bobble!", __func__); [self frobble_so]; [self bobble_so]; } @end </code></pre> You could optionally assert to ensure you are not sending the method to the wrong objects, or you could use <code>respondsToSelector:</code> instead of checking for protocol conformance. Whatever floats your boat, but this general tack should take you where you want to go.
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1. POHow do I define a category that adds methods to classes which implement a particular protocol?
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1. USJeremy W. Sherman
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1. USJeremy W. Sherman
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