UIView.layer.presentationLayer返回最终值(而不是当前值) [英] UIView.layer.presentationLayer returns final value (rather than current value)

问题描述

UIView子类中有一些相关代码:

- (void) doMyCoolAnimation {
  CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:@"position.x"];
  anim.duration = 4;
  [self.layer setValue:@200 forKeyPath:anim.keyPath];
  [self.layer addAnimation:anim forKey:nil];
}

- (CGFloat) currentX {
  CALayer* presLayer = self.layer.presentationLayer;
  return presLayer.position.x;
}

当我在动画运行时使用 [self currentX] 时，得到的是 200 (最终值)，而不是介于之间的值 0 (起始值)和 200 .是的，动画对用户可见，所以我在这里真的很困惑.

When I use [self currentX] while the animation is running, I get 200 (the end value) rather than a value between 0 (the start value) and 200. And yes, the animation is visible to the user, so I'm really confused here.

这是我调用 doMyCoolAnimation:以及1秒后 currentX 的代码.

Here's the code where I call doMyCoolAnimation:, as well as currentX after 1 second.

[self doMyCoolAnimation];

CGFloat delay = 1; // 1 second delay
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, 1 * NSEC_PER_SEC), dispatch_get_main_queue(), ^{
  NSLog(@"%f", [self currentX]);
});

有什么想法吗?

推荐答案

我的UIView图层的presentationLayer没有提供当前值.相反，它给了我动画的最终价值.

My UIView's layer's presentationLayer was not giving me the current values. It was instead giving me the end values of my animation.

 

要解决此问题，我要做的就是添加...

To fix this, all I had to do was add...

anim.fromValue = [self.layer valueForKeyPath:@"position.x"];

...对于我的 doMyCoolAnimation 方法之前，我将最终值设置为:

...to my doMyCoolAnimation method BEFORE I set the end value with:

[self.layer setValue:@200 forKeyPath:@"position.x"];

 

所以最后， doMyCoolAnimation 看起来像这样:

So in the end, doMyCoolAnimation looks like this:

- (void) doMyCoolAnimation {
  CABasicAnimation* anim = [CABasicAnimation animationWithKeyPath:@"position.x"];
  anim.duration = 4;
  anim.fromValue = [self.layer valueForKeyPath:anim.keyPath];
  [self.layer setValue:@200 forKeyPath:anim.keyPath];
  [self.layer addAnimation:anim forKey:nil];
}

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