此篇文章主要讲述了CALayer与动画相关的一些操作属性。

• CALayer的说明

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    /* The begin time of the object, in relation to its parent object, if
     * applicable. Defaults to 0. */
    
    public var beginTime: CFTimeInterval { get set }

    
    /* The basic duration of the object. Defaults to 0. */
    
    public var duration: CFTimeInterval { get set }

    
    /* The rate of the layer. Used to scale parent time to local time, e.g.
     * if rate is 2, local time progresses twice as fast as parent time.
     * Defaults to 1. */
    
    public var speed: Float { get set }

    
    /* Additional offset in active local time. i.e. to convert from parent
     * time tp to active local time t: t = (tp - begin) * speed + offset.
     * One use of this is to "pause" a layer by setting `speed' to zero and
     * `offset' to a suitable value. Defaults to 0. */
    
    public var timeOffset: CFTimeInterval { get set }

    
    /* The repeat count of the object. May be fractional. Defaults to 0. */
    
    public var repeatCount: Float { get set }

    
    /* The repeat duration of the object. Defaults to 0. */
    
    public var repeatDuration: CFTimeInterval { get set }

    
    /* When true, the object plays backwards after playing forwards. Defaults
     * to NO. */
    
    public var autoreverses: Bool { get set }

    
    /* Defines how the timed object behaves outside its active duration.
     * Local time may be clamped to either end of the active duration, or
     * the element may be removed from the presentation. The legal values
     * are `backwards', `forwards', `both' and `removed'. Defaults to
     * `removed'. */
    
    public var fillMode: String { get set }

beginTime 继承CAMediaTiming协议的对象的起始时间
duration 基本动画的持续时间
speed动画的运行速度，当为0时会停止动画，speed越大说明动画执行速度越快
timeOffset 动画的时间偏移，也就是上次动画的暂停/继续 距离本次动画的继续/暂停的时间差
repeatCount 重复次数
repeatDuration重复的时间
autoreverses是否会回到原来的位置
fillMode
CAFillModeRemoved 这个是默认值,也就是说当动画开始前和动画结束后,动画对layer都没有影响,动画结束后,layer会恢复到之前的状态
kCAFillModeForwards 当动画结束后,layer会一直保持着动画最后的状态
kCAFillModeBackwards 这个和kCAFillModeForwards是相对的,就是在动画开始前,你只要将动画加入了一个layer,layer便立即进入动画的初始状态并等待动画开始.你可以这样设定试代码,将一个动画加入一个layer的时候延迟5秒执行.然后就会发现在动画没有开始的时候,只要动画被加入了layer,layer便处于动画初始状态
kCAFillModeBoth 理解了上面两个,这个就很好理解了,这个其实就是上面两个的合成.动画加入后开始之前,layer便处于动画初始状态,动画结束后layer保持动画最后的状态.

• 下面进行实例演习
  做一个不停旋转的动画，通过点击事件控制动画的暂停或播放

    ///头像旋转,开始动画
    fileprivate func beginAnimation() {
        
        let rotateAnimation = CABasicAnimation(keyPath: "transform.rotation.z")
        rotateAnimation.fromValue = 0
        rotateAnimation.toValue = (Double.pi * 2)
        rotateAnimation.duration = 20
        rotateAnimation.repeatCount = MAXFLOAT
        singerImageView.layer.add(rotateAnimation, forKey: "")
    }

写一个CALayer的分类，控制动画的暂停与继续

extension CALayer {
    ///暂停动画
    func pauseAnimation() {
        //取出当前时间,转成动画暂停的时间
        let pausedTime = self.convertTime(CACurrentMediaTime(), from: nil)
        //设置动画运行速度为0
        self.speed = 0.0;
        //设置动画的时间偏移量，指定时间偏移量的目的是让动画定格在该时间点的位置
        self.timeOffset = pausedTime
    }
    ///恢复动画
    func resumeAnimation() {
        //获取暂停的时间差
        let pausedTime = self.timeOffset
        self.speed = 1.0
        self.timeOffset = 0.0
        self.beginTime = 0.0
        //用现在的时间减去时间差,就是之前暂停的时间,从之前暂停的时间开始动画
        let timeSincePause = self.convertTime(CACurrentMediaTime(), from: nil) - pausedTime
        self.beginTime = timeSincePause
    }
}

效果图如下：

animation.gif