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    <p>You will need to provide the C callback function within the Objective-C class implementation file, and this will only work if the callback is able to use a <em>context</em> pointer of some sort.</p> <p>So imagine the C callback signature is like this:</p> <pre><code>void myCallback(void *context, int someOtherInfo); </code></pre> <p>Then within the Objective-C class implementation file you need to use that callback to trampoline back into your Objective-C class (using the <em>context</em> pointer as the instance of the class to invoke):</p> <pre><code>// Forward declaration of C callback function static void theCallbackFunction(void *context, int someOtherInfo); // Private Methods @interface MyClass () - (void)_callbackWithInfo:(int)someOtherInfo; @end @implementation MyClass - (void)methodToSetupCallback { // Call function to set the callback function, passing it a "context" setCallbackFunction(theCallbackFunction, self); ... } - (void)_callbackWithInfo:(int)someOtherInfo { NSLog(@"Some info: %d", someOtherInfo); } @end static void theCallbackFunction(void *context, int someOtherInfo) { MyClass *object = (MyClass *)context; [object _callbackWithInfo:someOtherInfo]; } </code></pre> <p>If your C callback function does not accept some sort of <em>context</em> info, then:</p> <ol> <li>It's broken and this should be fixed/reported as a bug.</li> <li>You will need to rely on storing a <em>pointer-to-self</em> at global, static, scope to be used by the C callback function. This will limit the number of instances of <code>MyClass</code> to one!</li> </ol>
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    1. COI'd like to cast my vote that the phrase "trampoline back" somehow become the official term for this. It's awesome.
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    2. CO+1 - What if library doesn't provide params of `void* context`?
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    3. CO@MySpecialPurpose The term trampoline is an old one I'm afraid, and not my invention. I encountered it first when integrating C++ classes with thread creation functions, where such a trampoline method was required.
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