CALayer上的hitTest - 你如何找到被击中的实际图层？ [英] hitTest on CALayer - how do you find which actual layer was hit?

问题描述

情况：需要找到用户触摸的图层。

问题：Apple说我们应该使用[CALayer presentationLayer]进行命中测试，以便它表示当时屏幕上实际显示的内容（它捕捉动画中期等信息）。

...除了：presentationLayer不返回原始图层，它返回副本他们......所以：hitTest将返回一个全新的CALayer实例，该实例与原版不同。

我们如何找到实际的CALayer被击中？ / p>

例如

  CALayer * x = [CALayer layer]; 
 CALayer * y = [CALayer图层]; 
 [self.view.layer addSublayer：x]; 
 [self.view.layer addSublayer：y]; 
 
 ... 
 
 CALayer * touchingLayer = [self.view.layer.presentationLayer hitTest：touchPoint]; 
  

...但是，touchLayerx，还是y？

  if（touchingLayer == x）//这不起作用，因为来自Apple的touchLayer是 - 一个新对象
  

解决方案

啊！刚想通了这个问题，在CALayer的另一个问题上阅读邮件列表帖子。

调用[CALayer presentationLayer]后，使用图层的演示克隆 -tree，你可以在该树中获取任何对象，并在其上调用[CALayer modelLayer]以返回原始树中相同位置的原始参考对象。

这个参考是稳定的（测试 - 它可以工作）。

Apple的文档有点......模糊......在这一个。他们暗示它有时会失败（ ...结果未定义） - 但现在对我来说已经足够了。

Situation: need to find which layer the user has touched.

Problem: Apple says we should use [CALayer presentationLayer] to do hit-testing, so that it represents what is actually on screen at the time (it captures info mid-animation etc).

...except: presentationLayer does NOT return the original layers, it returns copies of them ... so: the hitTest will return a brand new CALayer instance that is not equivalent to the original.

How do we find which actual CALayer was hit?

e.g.

CALayer* x = [CALayer layer];
CALayer* y = [CALayer layer];
[self.view.layer addSublayer: x];
[self.view.layer addSublayer: y];

...

CALayer* touchedLayer = [self.view.layer.presentationLayer hitTest:touchPoint];

...but, is touchedLayer "x", or is it "y"?

if( touchedLayer == x ) // this won't work, because touchedLayer is - by definition from Apple - a new object

解决方案

Ah! Just figured this out, reading a mailing list post on a different problem with CALayer.

After calling [CALayer presentationLayer], and working with the "presentation clone" of the layer-tree, you can take any object in that tree, and call [CALayer modelLayer] on it to get back the original reference object at the same position in the original tree.

This reference is stable (tested - it works).

Apple's docs are a bit ... obscure ... on this one. And they imply it will "sometimes" fail ("...results are undefined") - but it's good enough for me for now.

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