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    <p>Go direct to the Objective-C runtime:</p> <pre><code>#import &lt;objc/runtime.h&gt; /* originally posted version — works because eventually class_getSuperclass(class) returns nil, and class_getSuperclass(nil) does so also. */ BOOL classDescendsFromClass(Class classA, Class classB) { while(1) { if(classA == classB) return YES; id superClass = class_getSuperclass(classA); if(classA == superClass) return (superClass == classB); classA = superClass; } } /* shorter version; exits straight after classA turns into nil */ BOOL classDescendsFromClassShorter(Class classA, Class classB) { while(classA) { if(classA == classB) return YES; classA = class_getSuperclass(classA); } return NO; } ... if(classDescendsFromClass(classToTest-&gt;isa, [NSObject class]) ... </code></pre> <p><code>class_getSuperclass</code> does what it says, and it's safe to compare metaclasses by pointer in the Objective-C runtime because there is only exactly one instance of the metaclass for each class. The isa pointer is the only thing that's definitely in struct objc_object.</p> <p>EDIT: additionally, there are known bugs in the iPhone simulator that cause some exceptions not to be caught by try/catch blocks. I've reported them as a bug to Apple and been told that mine was a duplicate, so they are definitely aware. Did you try your code on a real device or just in the simulator?</p> <p>EDIT2: from the wider context given elsewhere in this conversation, something like this might be smarter:</p> <pre><code>#import &lt;objc/runtime.h&gt; BOOL classRespondsToSelector(Class classA, SEL selector) { return class_getInstanceMethod(classA, selector) ? YES : NO; } .... if(classRespondsToSelector(instance-&gt;isa, @selector(respondsToSelector:)) { // great, we've got something that responds to respondsToSelector:; do the // rest of our querying through there } </code></pre>
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    1. POHow to tell if a Class inherits from NSObject (Objective-C)
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    1. COThis answer is excellent and works perfect. You're right about the try/catch blocks on the simulator/device too. I've read that try/catch blocks shouldn't be used to control flow (in obj-c), plus I'm not willing to lose simulator debugging, so I'll stick with this 'getSuperclass' concept.
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    2. COIt's not quite right actually; I allowed myself to become a tiny bit confused — NSObject's isa pointer points to NSObject (ie, even the NSObject metaclass is itself a subclass of NSObject), but NSObject is not a superclass of itself. So if(classA == superClass) terminates classDescendsFromClass one iteration later than necessary (because it eventually gets nil as a superclass of nil). I'll fix the code.
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    3. COIf you prefer more Obj-C like syntax: https://gist.github.com/BillinghamJ/6709374
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