详细分析frame、bounds、center、position、anchorPoint
iOS开发系列--让你的应用“动”起来
老司机带你走进Core Animation 之CAAnimation
iOS CoreAnimation 隐式动画

class ViewController: UIViewController {
    var cv: CusView!
    var bgLayer: CALayer!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
        let btn = UIButton(frame: CGRect(x: 50, y: 100, width: 200, height: 50 ))
        cv = CusView(frame: CGRect(x: 50  , y: btn.frame.maxY+20, width: 200, height: 200))
        cv.backgroundColor = .green
        self.view.addSubview(cv)
        bgLayer = CALayer()
        bgLayer.frame = cv.bounds
        cv.layer.addSublayer(bgLayer)
        
        
        btn.setTitle("changeColor", for: .normal)
        btn.backgroundColor = UIColor.gray
       
        view.addSubview(btn)
        btn.addTarget(self, action: #selector(clicked), for: .touchUpInside)

    }

    @objc func clicked(sender: UIButton) {

       case3()
    }
    func case1() {
        //CATransaction 只对layer生效，view无效
        CATransaction.begin()
        //        CATransaction.setDisableActions(true)
        CATransaction.setAnimationDuration(10)
        cv.layer.backgroundColor = UIColor.red.cgColor
        
        CATransaction.commit()
        CATransaction.setCompletionBlock {
            DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()+3) {
                self.cv.layer.backgroundColor = UIColor.green.cgColor
            }
        }
    }
    func case2() {
        //CATransaction 只对layer生效，view无效
        CATransaction.begin()
        //        CATransaction.setDisableActions(true)
        CATransaction.setAnimationDuration(10)
        bgLayer.backgroundColor = UIColor.red.cgColor
        
        CATransaction.commit()
        CATransaction.setCompletionBlock {
            DispatchQueue.main.asyncAfter(deadline: DispatchTime.now()+3) {
                self.bgLayer.backgroundColor = UIColor.green.cgColor
            }
        }
    }
    func case3() {
        let ani = CABasicAnimation(keyPath: "backgroundColor")
        ani.duration = 3
        ani.toValue = UIColor.red.cgColor
        ani.timeOffset = 3
        ani.isRemovedOnCompletion = false
        ani.fillMode = CAMediaTimingFillMode.forwards
        cv.layer.add(ani, forKey: "colorAnimate")
      
    }
}

class CusView: UIView,CAAction {
    func run(forKey event: String, object anObject: Any, arguments dict: [AnyHashable : Any]?) {
        print("event:\(event)  object:\(anObject)  dict:\(dict)")

        let temp: CALayer? = anObject as? CALayer
        guard let layer = temp else { return }
        if event == "position" && layer.position == CGPoint(x: 150,y: 270) {
            let ca = CABasicAnimation(keyPath: "position")
            ca.duration = 3
            ca.toValue = CGPoint(x: self.superview?.bounds.width ?? 0/2, y: self.superview?.bounds.height ?? 0/2)
            ca.fillMode = CAMediaTimingFillMode.forwards
            ca.isRemovedOnCompletion = false
            self.layer.add(ca, forKey: "move")
        }
    }
    

    /*
    // Only override draw() if you perform custom drawing.
    // An empty implementation adversely affects performance during animation.
    override func draw(_ rect: CGRect) {
        // Drawing code
    }
    */
    override func action(for layer: CALayer, forKey event: String) -> CAAction? {
        let action = super.action(for: layer, forKey: event)
//        print("key:\(event)")
        
        return action
    }

}

case1通过CATransaction 显示调用提交动画并没有生效（把v.layer.backgroundColor换成cv.backgroundColor）和case2却生效了，why？？？
通过customview override func action(for layer: CALayer, forKey event: String) -> CAAction? 断点，可以发现无论是修改view本身还是view持有的layer 都会走这个方法，并且返回了一个action为nil，so，并不会产生动画特效，UIview本身禁用了隐式动画的原因也是这个。UIView动画可以通过open class func animate(withDuration duration: TimeInterval, animations: @escaping () -> Void, completion: ((Bool) -> Void)? = nil)类似系统api去实现。也可以在这个接口的动画block里面和外面调用 action(for layer:CALayer ,forKey:String)看看得到的CAAction是否为nil。
而case2 是一个自定义的layer添加到view的layer上，这个自定义layer并没有把自己的CALayerDelegate交给任何对象，so，这个layer执行可以动画的属性时候不会走override func action(for layer: CALayer, forKey event: String) -> CAAction? 这个代理方法，而是去CALayer的Actions或者style字典搜索，然后去调用open class func defaultAction(forKey event: String) -> CAAction?，上面是一层层递进的如果返回结果为NSNull或者nil就会到下一步，如果最后一步仍返回nil，则无动画效果。
前面两个case，虽然我们通过代码去介入了，但具体动画怎么执行的还是有系统完成的，这种动画叫隐式动画，而case3是通过代码的方式添加具体动画行为，这种方式叫显示动画

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