CAShapeLayer shadowPath 动画。如何防止动画完成时的阴影填充？

Question

我正在创建一个随机的UIBezierPath，将路径设置为CAShapeLayer 的.path 属性，然后像这样为CAShapeLayer 的笔划设置动画：

    // Get a path
    let path = createBezierPath()

    // Shape layer properties
    let color = randomCGColor() // Color of path and shadow
    let lineWidth = CGFloat(arc4random_uniform(50) + 11) // Width of line and shadow radius
    shapeLayer.path = path.CGPath
    shapeLayer.lineJoin = kCALineJoinRound
    shapeLayer.lineCap = kCALineCapRound
    shapeLayer.strokeColor = color
    shapeLayer.lineWidth = lineWidth
    shapeLayer.fillColor = UIColor.clearColor().CGColor
    // Shape layer shadow properties
    shapeLayer.shadowPath = path.CGPath
    shapeLayer.shadowColor = color
    shapeLayer.shadowOffset = CGSizeZero
    shapeLayer.shadowRadius = lineWidth
    shapeLayer.shadowOpacity = 1.0

    // Add shape layer
    self.layer.addSublayer(shapeLayer)

    // Stroke path animation
    let pathAnimation: CABasicAnimation = CABasicAnimation(keyPath: "strokeEnd")
    pathAnimation.fromValue = 0.0
    pathAnimation.toValue = 1.0

    // Shadow path animation
    let shadowPathAnimation: CABasicAnimation = CABasicAnimation(keyPath: "shadowPath")
    shadowPathAnimation.fromValue = 0.0
    shadowPathAnimation.toValue = path.CGPath

    // Animation group
    let animationGroup = CAAnimationGroup()
    animationGroup.duration = 5.0
    animationGroup.animations = [pathAnimation, shadowPathAnimation]

    shapeLayer.addAnimation(animationGroup, forKey: "allMyAnimations")

问题是，一旦动画完成，阴影就会应用到整个形状。我希望阴影只应用于CAShapeLayer 的笔划。 如何防止动画完成后阴影应用到整个形状？

这是我所指问题的一个示例：

Answer 1

在this answer 的帮助下，我能够通过为阴影创建CALayer 并将CAShapeLayer 添加为子层来解决此问题：

    let path = createBezierPath() // Get a path
    let color = randomCGColor() // Color of path and shadow
    let lineWidth = CGFloat(arc4random_uniform(50) + 11) // Width of line and shadow radius

    // Shape layer properties
    shapeLayer.path = path.CGPath
    shapeLayer.lineJoin = kCALineJoinRound
    shapeLayer.lineCap = kCALineCapRound
    shapeLayer.strokeColor = color
    shapeLayer.lineWidth = lineWidth
    shapeLayer.fillColor = UIColor.clearColor().CGColor

    // Create shadow layer
    let shadowLayer = CALayer()
    shadowLayer.frame = self.bounds
    shadowLayer.shadowColor = color
    shadowLayer.shadowOffset = CGSizeZero
    shadowLayer.shadowRadius = lineWidth
    shadowLayer.shadowOpacity = 1.0
    shadowLayer.backgroundColor = UIColor.clearColor().CGColor
    shadowLayer.insertSublayer(shapeLayer, atIndex: 0)

    // Add shadow layer
    self.layer.addSublayer(shadowLayer)

    // Stroke path animation
    let pathAnimation: CABasicAnimation = CABasicAnimation(keyPath: "strokeEnd")
    pathAnimation.fromValue = 0.0
    pathAnimation.toValue = 1.0
    pathAnimation.duration = 5.0
    shapeLayer.addAnimation(pathAnimation, forKey: "strokeAnimation")

    // Shadow path animation
    let shadowPathAnimation: CABasicAnimation = CABasicAnimation(keyPath: "shadowPath")
    shadowPathAnimation.fromValue = 0.0
    shadowPathAnimation.toValue = path.CGPath
    shadowLayer.addAnimation(shadowPathAnimation, forKey: "shadowAnimation")

结果示例：