在UIView动画期间，CALayer Shadows消失

Question

So I'm currently testing out the UIView animations, and I noticed that the shadows rendered by CALayer (using [view.layer setShadowStuffHere] ) disappear at the start of the animation and reappear at the end of the animation. Is there any way I can keep these shadows and have the shadows animate along with the UIView? I tried using shadows without border paths, but that was a terrible idea, since the frame rate dropped like a rock during the animation, and I didn't get shadows anyways.

The code I'm using right now is below. Initially you see a red view, and when tapped, it'll flip over into a larger blue view. The end result should be something similar to the iPad music app; when an album is selected, it flips over to reveal a view on the backside.

- (void)viewDidLoad {
    [super viewDidLoad];

    UITapGestureRecognizer * tapRec;

    // Drop shadow Path creation
    CGFloat x1 = 0;
    CGFloat y1 = 0;
    CGFloat x2 = 100;
    CGFloat y2 = 100;

    frontBorderPath = CGPathCreateMutable();
    CGPathMoveToPoint(frontBorderPath, NULL, x1, y1);
    CGPathAddLineToPoint(frontBorderPath, NULL, x2, y1);
    CGPathAddLineToPoint(frontBorderPath, NULL, x2, y2);
    CGPathAddLineToPoint(frontBorderPath, NULL, x1, y2);
    CGPathAddLineToPoint(frontBorderPath, NULL, x1, y1);

    x2 = 400;
    y2 = 400;
    backBorderPath = CGPathCreateMutable();
    CGPathMoveToPoint(backBorderPath, NULL, x1, y1);
    CGPathAddLineToPoint(backBorderPath, NULL, x2, y1);
    CGPathAddLineToPoint(backBorderPath, NULL, x2, y2);
    CGPathAddLineToPoint(backBorderPath, NULL, x1, y2);
    CGPathAddLineToPoint(backBorderPath, NULL, x1, y1);

    containerView = [[UIView alloc] initWithFrame:CGRectMake(100, 100, 100, 100)];
    containerView.clipsToBounds = NO;
    [containerView.layer setShadowPath:frontBorderPath];
    [containerView.layer setShadowOpacity:1];
    [containerView.layer setShadowOffset:CGSizeMake(0,0)];
    [containerView.layer setShadowRadius:3];
    [containerView.layer setShouldRasterize:NO];
    [self.view addSubview:containerView];

    tapRec = [[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(frontTap)] autorelease];
    frontView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
    frontView.backgroundColor = [UIColor redColor];
    [frontView addGestureRecognizer:tapRec];
    [containerView addSubview:frontView];

    tapRec = [[[UITapGestureRecognizer alloc] initWithTarget:self action:@selector(backTap)] autorelease];
    backView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 400, 400)];
    backView.backgroundColor = [UIColor blueColor];
    [backView addGestureRecognizer:tapRec];    
}

- (void)frontTap{
    NSLog(@"fronttap");

    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.7];
    [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromRight forView:containerView cache:YES];

    [frontView removeFromSuperview];
    [containerView addSubview:backView];
    containerView.frame = CGRectMake(100, 100, 400, 400);
    [containerView.layer setShadowPath:backBorderPath];

    [UIView commitAnimations];

}

- (void)backTap{
    NSLog(@"backtap");

    [UIView beginAnimations:nil context:nil];
    [UIView setAnimationDuration:0.7];
    [UIView setAnimationTransition:UIViewAnimationTransitionFlipFromLeft forView:containerView cache:YES];

    [backView removeFromSuperview];
    [containerView addSubview:frontView];
    containerView.frame = CGRectMake(100, 100, 100, 100);
    [containerView.layer setShadowPath:frontBorderPath];

    [UIView commitAnimations];

}

Answer 1

事实证明，当你进行UIView动画时，它会忽略你视图的clipsToBounds属性并且无论如何都会剪辑它（至少对于翻转类型的动画），所以如果你想让你的阴影始终可见，你需要有一个足够大的视图框，包含所有内容。