Event handling between C++ and Objective C

Question

I recently started working on an iOS game and decided to write a distinct part of the project in C++. This approach seems to work fine as long as the Objective C classes simply access some members or call functions on the C++ objects. However i can't seem to find an elegant way to make my Objective C classes respond to 'events' in the C++ classes. Any event handling system that uses callbacks seems out of the question (since Objective C methods and C++ functions and probably not interchangeable). All i can think of is using the delegate pattern and writing wrapper classes around my C++ delegate classes so i can use them in Objective C code. So my question is: Is there a better way of doing this?

NB: I would like to prevent using Objective C directly in my C++ files, since these classes are supposed to be platform independent.

Answer 1

You may want to consider the mechanism that CoreVideo uses.

In their model, they have a mechanism which involves registering a C callback function( http://tinyurl.com/axtxajf ), and one of the parameters to this function is a void*, which can be typecast to the Objective-C class you need access to.

Here is an example of a C function you may implement in your C++ modules to register the callback function. The parameter are the callback function and the pointer to the class instance:

SetEventCallback(EventCallbackFunction, self);

When the event needs to be handled, the callback function is called, and you can typecast the void* to call Obj-C class and invoke the method:

void EventCallbackFunction(void* objCPtr)
{
    [(MyObjCClass*)objCPtr someMethod];
}

Answer 2

You could use C++0x lambda functions, they are interchangeable (assignable to each other) with Objective-C blocks.