iOS view淡入淡出切换

    CATransition *animation = [CATransition animation];
    animation.delegate = self;
    animation.duration = 0.7 ;  // 动画持续时间(秒)
    animation.timingFunction = UIViewAnimationCurveEaseInOut;
    animation.type = kCATransitionFade;//淡入淡出效果
        
    NSUInteger f = [[rView subviews] indexOfObject:fView];
    NSUInteger z = [[rView subviews] indexOfObject:zView];
    [rView exchangeSubviewAtIndex:z withSubviewAtIndex:f];
    
    [[rView layer] addAnimation:animation forKey:@"animation"];    CATransition *animation = [CATransition ani