完成后如何重新启动 CABasicAnimation

Question

我有一个按钮，按下它会在 2 秒内运行 CABasicAnimation。我第一次按下按钮时，动画运行良好，图层被填充为红色。我第二次按下按钮动画不再运行。红色层消失了，因为我删除了它，但它并没有从头开始。

在下面的代码中，basicAnimation 是一个类属性。我还尝试在 buttonPressed 方法本身中创建它，这没有任何区别，然后我尝试将其添加为可选的var basicAnimation: CABasicAnimation?，在 buttonPressed 方法中对其进行实例化，然后在 animationDidStop(_:finished:) 委托方法中将其设置为 nil，但均未成功。

为什么不再运行？

let shapeLayer = CAShapeLayer()

let basicAnimation = CABasicAnimation(keyPath: "strokeEnd")
// var basicAnimation: CABasicAnimation? // I tried this

override func viewDidLoad() {
    super.viewDidLoad()

    let circularPath = UIBezierPath(arcCenter: view.center, radius: 100, startAngle: -.pi/2, endAngle: 3 * .pi/2, clockwise: true)
    shapeLayer.path = circularPath.cgPath
    shapeLayer.strokeColor = UIColor.red.cgColor
    shapeLayer.fillColor = UIColor.clear.cgColor
    shapeLayer.lineWidth = 10
    shapeLayer.strokeEnd = 0
    view.layer.addSublayer(shapeLayer)
}

@objc func buttonTapped() {

    // basicAnimation = CABasicAnimation(keyPath: "strokeEnd") // I tried this
    // let basicAnimation = CABasicAnimation(keyPath: "strokeEnd") // I also tried this
    removeAnimation()

    basicAnimation.delegate = self
    basicAnimation.timingFunction = CAMediaTimingFunction(name: CAMediaTimingFunctionName.default)
    basicAnimation.fromValue = 0
    basicAnimation.toValue = 1
    basicAnimation.duration = CFTimeInterval(2)
        
    basicAnimation.fillMode = CAMediaTimingFillMode.forwards
    basicAnimation.isRemovedOnCompletion = false
        
    shapeLayer.add(basicAnimation, forKey: "myAnimation")
}

func removeAnimation() {
    shapeLayer.removeAnimation(forKey: "myAnimation")
}

func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
    print("animation done") // prints once

    // basicAnimation = nil // I tried this
}

Answer 1

每次点击按钮时都制作一个新动画，我就能让您的代码正常工作：

let shapeLayer = CAShapeLayer()

var basicAnimation: CABasicAnimation!

override func viewDidLoad() {
    super.viewDidLoad()

    let circularPath = UIBezierPath(arcCenter: view.center, radius: 100, startAngle: -.pi/2, endAngle: 3 * .pi/2, clockwise: true)
    shapeLayer.path = circularPath.cgPath
    shapeLayer.strokeColor = UIColor.red.cgColor
    shapeLayer.fillColor = UIColor.clear.cgColor
    shapeLayer.lineWidth = 10
    shapeLayer.strokeEnd = 0
    view.layer.addSublayer(shapeLayer)
}

@IBAction func buttonTapped(_ sender: Any) {

    basicAnimation = CABasicAnimation(keyPath: "strokeEnd")
    removeAnimation()

    basicAnimation.delegate = self
    basicAnimation.timingFunction = CAMediaTimingFunction(name: CAMediaTimingFunctionName.default)
    basicAnimation.fromValue = 0
    basicAnimation.toValue = 1
    basicAnimation.duration = CFTimeInterval(2)
        
    basicAnimation.fillMode = CAMediaTimingFillMode.forwards
    basicAnimation.isRemovedOnCompletion = false
        
    shapeLayer.add(basicAnimation, forKey: "myAnimation")
}

func removeAnimation() {
    shapeLayer.removeAnimation(forKey: "myAnimation")
}

func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
    print("animation done")
}