暂停以及继续动画

ios developer core animation programming guide - advanced animation tricks

• pausing and resuming animations

    func pauseAnimation() {
        let pausedTime = layer.convertTime(CACurrentMediaTime(), fromLayer: nil)
        layer.speed = 0
        layer.timeOffset = pausedTime
    }
    
    func resumeAnimation() {
        let pausedTime = layer.timeOffset
        layer.speed = 1
        layer.timeOffset = 0
        layer.beginTime = 0
        let timeSincePause = layer.convertTime(CACurrentMediaTime(), fromLayer: nil) - pausedTime
        layer.beginTime = timeSincePause
    }