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POConditionally overriding a system method via categories in Objective-C?
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copied!<p>Is there a way to provide a method implementation (that bears the exact same name of a method defined by the framework) only when the method isn't already defined in the system? For example method <code>[NSSomeClass someMethod:]</code> exists only in Mac OS X 10.6 and if my app runs in 10.5, I will provide that method's definition in a category. But when the app runs in 10.6, I want the OS-provided method to run.</p> <p><strong>Background:</strong> I'm creating an app targeted for both 10.5 and 10.6. The problem is that I recently realized that method <code>+[NSSortDescriptor sortDescriptorWithKey:ascending:]</code> only exists in 10.6 and my code is already littered by that method call. I could provide a default implementation for it (since this time it's not too difficult to implement it myself), but I want the "native" one to be called whenever my app runs on 10.6. Furthermore if I encounter similar problems in the future (with more difficult-to-implement-myself methods), I might not be able to get away with providing a one-liner replacement.</p> <p>This question vaguely similar to <a href="https://stackoverflow.com/questions/1085479/override-a-method-via-objc-category-and-call-the-default-implementation">Override a method via ObjC Category and call the default implementation?</a> but the difference is that I want to provide implementations only when the system doesn't already have one.</p> <p>Thanks.</p>

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