如何键值观察CALayer的旋转? [英] How to Key-Value-Observe the rotation of a CALayer?

问题描述

我可以这样访问该值:

NSNumber* rotationZ = [myLayer valueForKeyPath:@"transform.rotation.z"];

但是由于某些原因，如果我尝试KV观察该关键路径，则会出现编译器错误.首先，这是我尝试做到的方式:

But for some reason, if I try to KV-observe that key path, I get a compiler error. First, this is how I try to do it:

[myLayer addObserver:self forKeyPath:@"transform.rotation.z" options:0 context:nil];

编译器告诉我:

***由于未捕获的异常'NSUnknownKeyException'而终止应用程序， 原因: '[ addObserver:forKeyPath:@"rotation.z" 已发送选项:0x0上下文:0x528890] 到不符合KVC的对象 旋转"属性."

*** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[ addObserver: forKeyPath:@"rotation.z" options:0x0 context:0x528890] was sent to an object that is not KVC-compliant for the "rotation" property.'

我不明白的是，为什么我可以通过KVC密钥路径访问z值，但不向其添加观察者.这有道理吗?

what I don't get is, why I can access that z value by KVC key path, but not add an observer to it. Does this make sense?

我还能如何观察该矩阵的z值?我不在乎矩阵的其他值.仅z旋转.还有其他方式可以访问和观察它吗?

How else could I observe the z value of that matrix? I don't care about the other values of the matrix. Only the z rotation. Any other way to access and observe it?

推荐答案

CALayer的transform属性是结构，而不是对象，因此不符合KVC.

The transform property for the CALayer is a struct, not an object, so it isn't KVC compliant.

您应该能够做的是，而不是绑定到Z旋转，而是绑定到transform属性，并在每次收到KVO通知时将Z值拉出.

What you should be able to do is, instead of binding to the Z rotation, bind to the transform property and pull the Z value out whenever you get the KVO notification.

我认为这里的困惑在于，当您在NSObject上使用点表示法时，您实际上是在使用该对象的- (id)property和- (void)setProperty方法，这些方法与KVC兼容.在结构上使用点表示法时，就是在访问该结构的成员，而不是调用方法.

I think the confusion here is that when you use dot notation on an NSObject, you're really using that object's - (id)property and - (void)setProperty methods, which are KVC compliant. When you use dot notation on a struct, you're accessing a member of that struct, not calling a method.

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