Accessing an ObjC object from a C function callback

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!

Dave DeLong · Accepted Answer · 2011-06-02 19:55:33Z

8

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? ;)}

edited Jun 2, 2011 at 19:55

answered Jun 2, 2011 at 19:45

Dave DeLong

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x4u · Accepted Answer · 2011-06-02 19:46:50Z

5

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.

answered Jun 2, 2011 at 19:46

x4u

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Comments

Chanok · Accepted Answer · 2011-06-02 20:28:33Z

3

Example code

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

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

answered Jun 2, 2011 at 20:28

Chanok

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