Core Animation(核心动画) 中KeyPath的取值

在Core Animation中， 借助Core Animation 提供的几个动画类我们可以对一个Layer做各种酷炫的动画，在实例 CAPropertyAnimation 的时候（ CABasicAnimation 和 CAKeyFrameAnimation均继承自该类），通过构造方法 convenience init(keyPath path: String?)，需要传入一个字符串。 那么问题来了，这个参数到底可以取哪些值呢？

我们知道 CALayer 实现了 NSKeyValueCoding 协议，因此我们可以使用 KVC 对 CALayer的实例中的属性进行取值和赋值，而在 Core Animation 提供的几个动画类影响的对象便是 CALayer的实例，我们可以推测在 CAPropertyAnimation 类中构造方法 convenience init(keyPath path: String?) 的keyPath参数的取值 应该是 CALayer 中的属性。 带着这个推测，参考苹果的官方文档，笔者把可以用作keyPath的值列举如下。

一、可动画属性

1. 几何属性 (Geometry Properties)

Field Key Path	Remark	En Description
transform.rotation.x	按x轴旋转的弧度	Set to an NSNumber object whose value is the rotation, in radians, in the x axis.
transform.rotation.y	按y轴旋转的弧度	Set to an NSNumber object whose value is the rotation, in radians, in the y axis.
transform.rotation.z	按z轴旋转的弧度	Set to an NSNumber object whose value is the rotation, in radians, in the z axis.
transform.rotation	按z轴旋转的弧度, 和transform.rotation.z效果一样	Set to an NSNumber object whose value is the rotation, in radians, in the z axis. This field is identical to setting the rotation.z field.
transform.scale.x	在x轴按比例放大缩小	Set to an NSNumber object whose value is the scale factor for the x axis.
transform.scale.y	在x轴按比例放大缩小	Set to an NSNumber object whose value is the scale factor for the y axis.
transform.scale.z	在z轴按比例放大缩小	Set to an NSNumber object whose value is the scale factor for the z axis.
transform.scale	按比例放大缩小	Set to an NSNumber object whose value is the average of all three scale factors.
transform.translation.x	沿x轴平移	Set to an NSNumber object whose value is the translation factor along the x axis.
transform.translation.y	沿y轴平移	Set to an NSNumber object whose value is the translation factor along the y axis.
transform.translation.z	沿z轴平移	Set to an NSNumber object whose value is the translation factor along the z axis.
transform.translation	x,y 坐标均发生改变	Set to an NSValue object containing an NSSize or CGSize data type. That data type indicates the amount to translate in the x and y axis.
transform	CATransform3D 4*4矩阵
bounds	layer大小
position	layer位置
frame	不支持 frme 属性	computed from the bounds and position and is NOT animatable
anchorPoint	锚点位置
cornerRadius	圆角大小
zPosition	z轴位置

2.背景属性 (Background Properties)

Field Key Path	Remark	En Description
backgroundColor	背景颜色

3.Layer内容 (Layer Content)

Field Key Path	Remark	En Description
contents	Layer内容，呈现在背景颜色之上
contentsRect		The rectangle, in the unit coordinate space, that defines the portion of the layer’s contents that should be used.
masksToBounds		setting the layer’s masksToBounds property to YES does cause the layer to clip to its corner radius

4.子Layer内容 (Sublayers Content)

Field Key Path	Remark	En Description
sublayers	子Layer数组
sublayerTransform	子Layer的Transform	Specifies the transform to apply to sublayers when rendering.

5.边界属性 (Border Attributes)

Field Key Path	Remark	En Description
borderColor
borderWidth

6.阴影属性 (Shadow Properties)

Field Key Path	Remark	En Description
shadowColor	阴影颜色
shadowOffset	阴影偏移距离
shadowOpacity	阴影透明度
shadowRadius	阴影圆角
shadowPath	阴影路径

7.透明度 (Opacity Property)

Field Key Path	Remark	En Description
opacity	透明度
hiden

8.遮罩 (Mask Properties)

Field Key Path	Remark	En Description
mask

9.ShapeLayer属性 (ShapeLayer)

Field Key Path	Remark	En Description
fillColor
strokeColor
strokeStart	从无到有
strokeEnd	从有到无
lineWidth	路径的线宽
miterLimit	相交长度的最大值
lineDashPhase	虚线样式

二、注意

这里特别需要注意的是 layer的 frame 是不支持动画的，我们可以通过改变position和````bounds``` 变通实现

三、参考资料

• Apple Key-Value Coding Extensions

• Layer Animatable Properties

• How can I know the values in CABasicAnimation keyPath?

• What is the role of key path in Core Animation?