如何在 UIImageView 旋转期间动态调整阴影？

Question

我使用以下代码来添加投影：

letterE.layer.shadowColor = [[UIColor blackColor] CGColor];
letterE.layer.shadowOffset = CGSizeMake(2.5, 2.5);
letterE.layer.shadowRadius = 3.0;
letterE.layer.shadowOpacity = 0.95;

并使用以下代码来旋转：

CABasicAnimation* rotationAnimation;
rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
rotationAnimation.toValue = [NSNumber numberWithFloat: M_PI * 2.0];
rotationAnimation.duration = 5.0;
rotationAnimation.cumulative = YES;
rotationAnimation.repeatCount = 1.0; 
rotationAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];

[letterE.layer addAnimation:rotationAnimation forKey:@"rotationAnimation"];

在动画期间，阴影是静态的，看起来很奇怪：

如何使阴影在动画过程中动态更新？

Answer 1

我发现这很有趣，所以我尝试了一下。一种可能的解决方案是在主视图下构建第二个清晰视图，使用原始视图的路径为其（底部视图）提供阴影。然后您可以将动画应用到两个视图。我使用简单的矩形视图完成了此操作，但我认为没有理由不能使用更复杂的路径或使用 2 个 CALayers 而不是 2 个 UIView 来完成此操作。

这就是我设置视图的方式...

testView = [[UIView alloc] initWithFrame:CGRectMake(40, 40, 100, 100)];
testView.backgroundColor = [UIColor redColor];

//increase y origin of second view to simulate shadow offset
testViewShadow = [[UIView alloc] initWithFrame:CGRectMake(40, 50, 100, 100)];

CGMutablePathRef path = CGPathCreateMutable();
CGPathAddRect(path, NULL, CGRectMake(0, 0, testView.frame.size.width, testView.frame.size.height)); 
testViewShadow.layer.shadowPath = path;
testViewShadow.layer.shadowOpacity = 1.0;
testViewShadow.layer.shadowOffset = CGSizeMake(0, 0);
testViewShadow.layer.shadowRadius = 10.0;
CFRelease(path);

[self.view addSubview:testViewShadow];
[self.view addSubview:testView];

以及我的动画（只需将 CAAnimation 作为 IBAction 连接到按钮并应用于两个视图）...

- (IBAction)rotate:(id)sender{
    CABasicAnimation* rotationAnimation;
    rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    rotationAnimation.toValue = [NSNumber numberWithFloat: M_PI * 2.0];
    rotationAnimation.duration = 5.0;
    rotationAnimation.cumulative = YES;
    rotationAnimation.repeatCount = 1.0; 
    rotationAnimation.timingFunction = [CAMediaTimingFunction functionWithName:kCAMediaTimingFunctionEaseOut];

    [testView.layer addAnimation:rotationAnimation forKey:@"rotationAnimation"];
    [testViewShadow.layer addAnimation:rotationAnimation forKey:@"rotationAnimation"];
}

这就是结果的样子...

任何（2D）变换都应该如果将它们应用到这两种视图中，看起来会很可信。

希望有帮助！