When do UIAppearance proxy rules get applied to new view controller?

问题

I'm wandering when exactly do UIAppearance rules get applied to some new view controller?

I've made some global rules and I call them in my app delegate. That way all UIButtons look that same. But now I want to modify just appearance of one UIButton. I've tried putting the code to remove it's background inside - (void)viewDidLoad but it's not working - UIAppearance rules aren't applied yet. In one ViewController I put modification code inside - (void)viewWillLayoutSubviews and it worked perfectly, but now in another ViewController it doesn't work (code is the same).

Where is it safe to override UIAppearance rules?

回答1:

According to the 2011 WWDC video introducing UIAppearance, the customizations are applied right before -layoutSubviews is called on the view.

回答2:

If you're looking to customise one specific button you should either:

1. Alter the properties of the button instance directly, and not touch the appearance settings for the class, or

2. Use the appearanceWhenContainedIn: method like below:

   [[UIButton appearanceWhenContainedIn:[CustomView class], nil]
    setBackgroundImage:myButtonImage
               forState:UIControlStateNormal];
   

That way you can still use the appearance proxy for your specific button (when you know it's contained in a specific view), and not alter the general appearance settings.

来源：https://stackoverflow.com/questions/11471362/when-do-uiappearance-proxy-rules-get-applied-to-new-view-controller