通过给继承与 UIImageView 的类 CXGImageView 添加 CABasicAnimation 转动动画,实现播放器图片转动效果.

主要提供三个方法: startRotating, stopRotating,resumeRotate

startRotating

/// 开始动画
func startRotating() {
 let rotateAnimation = CABasicAnimation(keyPath: "transform.rotation")
 rotateAnimation.isRemovedOnCompletion = false // 避免点击 Home 键返回,动画停止
 rotateAnimation.fromValue = 0.0
 rotateAnimation.toValue = Double.pi * 2
 rotateAnimation.duration = 20
 rotateAnimation.repeatCount = MAXFLOAT
 self.layer.add(rotateAnimation, forKey: nil)
 isRotating = true
}

stopRotating

/// 停止动画
func stopRotating() {
 if !isRotating {
 return
 }
 let pausedTime = self.layer.convertTime(CACurrentMediaTime(), from: nil)
 // 让CALayer的时间停止走动
 self.layer.speed = 0
 // 让CALayer的时间停留在pausedTime这个时刻
 self.layer.timeOffset = pausedTime
 isRotating = false
}

resumeRotate

/// 继续动画
func resumeRotate() {

 if isRotating {
 return
 }

 if self.layer.timeOffset == 0 {
 startRotating()
 return
 }

 let pausedTime = self.layer.timeOffset
 // 1. 让CALayer的时间继续行走
 self.layer.speed = 1.0
 // 2. 取消上次记录的停留时刻
 self.layer.timeOffset = 0.01
 // 3. 取消上次设置的时间
 self.layer.beginTime = 0.0
 // 4. 计算暂停的时间(这里也可以用CACurrentMediaTime()-pausedTime)
 let timeWhenpause = self.layer.convertTime(CACurrentMediaTime(), from: nil) - pausedTime
 // 5. 设置相对于父坐标系的开始时间(往后退timeSincePause)
 self.layer.beginTime = timeWhenpause
 isRotating = true

}

注意: 使用中发现,当点下 Home 键再次返回应用时,图片停止转动,需要将动画 isRemovedOnCompletion 置成 false.