Can't find UI_APPEARANCE_SELECTOR anywhere

Question

iOS documentation of UIAppearanceContainer Protocol Reference says:

"To participate in the appearance proxy API, tag your appearance property accessor methods in your header with UI_APPEARANCE_SELECTOR."

But when I, for example, open UIButton.h, I can't find anywhere UI_APPEARANCE_SELECTOR, although I can use something like this wihout problems:

    [[UIButton appearance] setBackgroundImage:[[UIImage imageNamed:@"UIButton"] resizableImageWithCapInsets:UIEdgeInsetsMake(5.0, 5.0, 5.0, 5.0)] forState:UIControlStateNormal];

Can anyone tell me what's going on :D ?

Answer 1

You can't find it because the accessor is inherited from UIView (UIButton inherits from; UIControl : UIView : UIResponder : NSObject). So when you're doing [UIButton appearance] you get the appearance proxy for the passed class, just because UIView adopts the UIAppearance and UIAppearanceContainer protocols. I hope that this makes sense.

PS. If you look for example UIBarButtonItem's header file, you will see that the UI_APPEARANCE_SELECTOR is there.