在 UIView 动画期间观察键值 [英] Key value Observing during UIView Animations

问题描述

我正在为程序中的视图的 center 属性设置动画.在动画过程中，当中心达到特定值时我需要通知.

I'm animating the center property of a view in my program. During the animation, I need notifications when center hits a particular value.

我尝试将自己添加为 view 的 center 属性的键值观察者.但是，我只在动画开始时收到通知.所以我无法检测物体是否/何时通过我的兴趣点.

I tried adding the myself as a key value observer for the center property of the view . However, I only get notified when the animation begins. So I'm unable to detect if/when the object passes through my point of interest.

有没有办法通过 KVO 或任何其他方法来做到这一点?

Is there a way to do this through KVO or any other method?

谢谢！

推荐答案

您可以通过访问表示层来检索表示 UIView 动画层当前状态的值.这可以使用如下代码完成:

You can retrieve the values representing the current state of the UIView's animating layer by accessing its presentation layer. This can be done using code like the following:

CGPoint currentCenter = [[view.layer presentationLayer] center];

不幸的是，表示层的属性不符合 KVO，因此我能想到的跟踪当前值的最佳方法是不断轮询表示层，直到它靠近您想要的位置.

Unfortunately, the presentation layer's properties are not KVO-compliant, so the best way I can think of for tracking the current value is to keep polling the presentation layer until it gets near the location you want.

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