CAShapeLayer shadowPath animation. How to prevent shadow fill on animation completion?

Question

I'm creating a random UIBezierPath, setting the path to a CAShapeLayer's .path property, and then animating the CAShapeLayer's stroke like so:

    // 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")

The issue is, once the animation completes the shadow is applied to the entire shape. I'd like the shadow to just be applied to the CAShapeLayer's stroke. How can I prevent the shadow from applying to the entire shape after the animation completes?

Here's an example of the issue I'm referring to:

Answer 1

I was able to solve the issue, with the help of this answer, by creating a CALayer for the shadow and adding the CAShapeLayer as a sublayer:

    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")

Example of the result: