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POforwardInvocation to other class instead of instance
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  1. POforwardInvocation to other class instead of instance
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    copied!<p>I have a <a href="http://en.wikipedia.org/wiki/Facade_pattern" rel="nofollow">facade</a> singleton that I'd like to forward some class method calls to some "static" class.</p> <p>At first glance, <code>forwardInvocation:</code> appeared to be a possible solution, however, <code>NSInvocation</code>'s <code>invokeWithTarget:</code> and <code>setTarget:</code> only accept an <code>id</code>, i. e. a pointer to an instance, not a class itself. I tried handing over <code>[MyTargetClass class]</code> as the target, but I still get a "No known class method [...]" error when I call <code>[Facade someForwardedMethod]</code> somewhere. When I call <code>[[Facade sharedInstance] someForwardedMethod]</code> I get a "No visible @interface [...] declares the selector [...]" error.</p> <p>Of course I am aware that I also need to override <code>respondsToSelector:</code> and <code>methodSignatureForSelector:</code>, so my code looks like this:</p> <pre><code>- (BOOL)respondsToSelector:(SEL)aSelector { if ([super respondsToSelector:aSelector]) { return YES; } else { return [MyTargetClass respondsToSelector:aSelector]; } } - (NSMethodSignature *)methodSignatureForSelector:(SEL)selector { NSMethodSignature* signature = [super methodSignatureForSelector:selector]; if (!signature) { signature = [MyTargetClass methodSignatureForSelector:selector]; } return signature; } - (void)forwardInvocation:(NSInvocation *)anInvocation { SEL aSelector = [anInvocation selector]; if ([MyTargetClass respondsToSelector: aSelector]) { [anInvocation invokeWithTarget:[MyTargetClass class]]; } else { [super forwardInvocation:anInvocation]; } } </code></pre> <p>Is there a way to make this work, or do I have to choose another approach?</p> <hr> <p>EDIT: I have tried both ways that Rob Napier mentions in his answer, here are my findings:</p> <p>I can call a class method in my target class through the facade instance with</p> <pre><code>[(id)[Facade sharedInstance] doSomethingClassyInTargetClass]; </code></pre> <p>It's a bit uglier than I hoped for, but it works. However, I can not call a class method in my target class when I address the facade class. To quieten the compiler I can write</p> <pre><code>[(Class)[Facade class] doSomethingClassyInTargetClass]; </code></pre> <p>but then it throws an 'NSInvalidArgumentException' "[Facade doSomethingClassyInTargetClass]: unrecognized selector sent to class [...]" at runtime. Apparently the class methods of the facade class get resolved without respect for <code>forwardInvocation:</code>, but after all it has a <code>-</code> in front...</p>
 

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