Accessing an ObjC object from a C function callbac

Question

I'm playing around a bit with global hot keys in Carbon, and I registered a hot key. When the hot key is pressed, this function is called:

OSStatus myHotKeyHandler(EventHandlerCallRef nextHandler, EventRef anEvent, void *userData) {
    ...
}

This function is in the same file as my app delegate's definition. How do I now call an ObjC method on my delegate in that function?

[self aMethod];

I cant add a void* (to be a pointer to my class instance) to the C function, because I am not the one calling it.

I tried to convert the method into a class method and then call it with [AppDelegate aFunction], which works but then I cant use my instance variables!

Answer 1

You're reinventing the wheel. Use a wrapper:

http://github.com/davedelong/DDHotKey

_{well perhaps not a wheel, since hot keys aren't "trivial" concepts. maybe you're reinventing a differential? or something? ;)}

Answer 2

Example code

InstallApplicationEventHandler(&MyHotKeyHandler,1,&eventType,(void *)self,NULL);
...

OSStatus MyHotKeyHandler(EventHandlerCallRef nextHandler,EventRef theEvent,
                         void *userData)
{
    [(yourAppDelegate *)userData dosomething];
}

Answer 3

Give the pointer to your class instance as parameter for userData when you register your event handler. You will then get this pointer back inside the handler as userData.