但是這裡介面切換的實現全部由UITabBarController，也就是系統自動幫你來實現了，要在哪裡新增動畫程式碼呢？

很簡單，寫一個類繼承自UITabBarController，然後實現下面這個委託方法就行了:

CATransition* animation = [CATransition animation];
        [animation setDuration:0.5f];
        [animation setType:kCATransitionFade];
        [animation setSubtype:kCATransitionFromRight];
        [animation setTimingFunction:[CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut]];
        [[self.view layer]addAnimation:animation forKey:@"switchView"];