从动画视图中获取 transform.rotation.z 值

Question

我正在使用CABasicAnimation 连续旋转UIImageView，我希望能够获得旋转角度。

-(void)viewDidAppear:(BOOL)animated{

    [self spinAnimationOnView:self.myImageView
                        duration:2
                          repeat:HUGE_VAL];
}

- (void)spinAnimationOnView:(UIView*)view duration:(CGFloat)duration repeat:(float)repeat{
    CABasicAnimation* rotationAnimation;
    rotationAnimation = [CABasicAnimation animationWithKeyPath:@"transform.rotation.z"];
    rotationAnimation.toValue = [NSNumber numberWithFloat: M_PI * 2.0];
    rotationAnimation.duration = duration;
    rotationAnimation.repeatCount = repeat;

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

动画按预期运行。但后来我尝试得到这样的旋转角度：

CGFloat angle = [(NSNumber *)[self.myImageView valueForKeyPath:@"layer.transform.rotation.z"] floatValue];

NSLog(@"ROTATION = %f", angle);

输出始终为 0。有什么想法吗？

Answer 1

在动画进行时，您需要使用 CALayer 的presentationLayer 来获取图层的状态。请参阅CALayer docs。

CGFloat angle = [[self.myImageView valueForKeyPath:@"layer.presentationLayer.transform.rotation.z"] floatValue];

NSLog(@"ROTATION = %f", angle);