iPhone dev - How far down should I cast?

Question

If I have a method that passes an argument of type void * (UIView animation did stop method, has to be a void pointer), or of type id, and I know that the argument is a UIBarButton item, and I need to disable it, [barbuttonitem setEnabled:NO];, should I cast the argument to a UIControl, which is as far as I need to be able to use setEnabled (without a warning), or should I cast it all the way down to UIBarButtonItem? Why?

Thanks!!

Answer 1

I'd say cast it to a UIControl, just in case the implementation changes at some point. I'd always cast to the most appropriate interface (not implementation), and UIControl is probably the way to go.

Answer 2

Casting is only telling the compiler that you are expecting a variable of a certain type: It does not cause any changes in the variable passed in. You can cast it to UIBarButtonItem without worries.

Answer 3

UIBarItem is not derived from UIControl, so casting to UIControl really isn't the correct thing to do. It works because both classes happen to have setEnabled: methods.

Casts are just another form of documentation; they don't affect what happens at runtime. If you're expecting a UIBarItem then cast it as such.

Answer 4

If i understand Objective-C correctly, you can call setEnabled directly on the object; you just won't get a guarantee that the call will go through. But if you know that the object returned is a UIBarItem then you can call it.