IOS Animation-CAKeyframeAnimation例子（简单动画实现）

 1     //让一个layer左右晃动
 2     func addLayerKeyframeAnimationRock(layer:CALayer) {
 3         let animation = CAKeyframeAnimation(keyPath: "position.x")
 4         animation.values = [0, 10, -10, 0]
 5         //additive设置为true是使Core Animation 在更新 presentation layer 之前将动画的值添加到 model layer 中去。可以看到上面的values是0，10，-10，0. 没有设置的话values=layer.position.x+0, layer.position.x+10, layer.position.x-10
 6         animation.additive = true
 7         animation.duration = 0.3
 8         animation.repeatCount = 999999
 9         
10         layer.addAnimation(animation, forKey: "addLayerKeyframeAnimationRock")
11     }

 1     //让一个layer圆周（圆圈）运动
 2     func addLayerKeyframeAnimationOrbit(layer:CALayer) {
 3         let animation = CAKeyframeAnimation(keyPath: "position")
 4         let boundingRect = CGRectMake(layer.frame.origin.x, layer.frame.origin.y, 100, 100)
 5         animation.path = CGPathCreateWithEllipseInRect(boundingRect,nil)
 6         animation.duration = 3
 7         animation.repeatCount = HUGE
 8         //其值为kCAAnimationPaced，保证动画向被驱动的对象施加一个恒定速度，不管路径的各个线段有多长，并且无视我们已经设置的keyTimes
 9         animation.calculationMode = kCAAnimationPaced
10         //kCAAnimationRotateAuto，确定其沿着路径旋转（具体要自己来体验，这里难解释）
11         animation.rotationMode = kCAAnimationRotateAuto
12         
13         layer.addAnimation(animation, forKey: "addLayerKeyframeAnimationOrbit")
14     }