CAShapelayer Duplicates - swift

Question

I'm trying to add a CAShapelayer once every 20ms to given x and y coordinates. I would like the shape to fade away over a second (like a tracer). The function I have created works, the shape is created in the correct location and fades away. But I am getting extra shapes left behind cluttering up the screen.
func shadowBall (x: CGFloat, y: CGFloat){
let xpos : CGFloat = ((self.frame.width/2) + x)
let ypos : CGFloat = ((self.frame.height/2) + y)
let shadowBall = CAShapeLayer()
let shadowBalllRadius :CGFloat = 4
let shadowBallPath : UIBezierPath = UIBezierPath(ovalInRect: CGRect(x: xpos, y: ypos, width: CGFloat(shadowBalllRadius*2), height: CGFloat(shadowBalllRadius*2)))
shadowBall.path = shadowBallPath.CGPath
shadowBall.fillColor = UIColor.clearColor().CGColor
shadowBall.strokeColor = UIColor.whiteColor().CGColor
shadowBall.lineWidth = 0.5
let animation: CABasicAnimation = CABasicAnimation(keyPath: "strokeColor")
animation.fromValue = UIColor.whiteColor().CGColor
animation.toValue = UIColor.clearColor().CGColor
animation.duration = 1.0;
animation.repeatCount = 0;
animation.removedOnCompletion = true
animation.additive = false
self.layer.addSublayer(shadowBall)
shadowBall.addAnimation(animation, forKey: "strokeColor")
}

Answer 1

The problem is that when the animation finishes, it restores the strokeColor to the original color. You should really set the strokeColor of the original shape layer to be clearColor(), that way, when you finish animating from whiteColor() to clearColor(), it will remain at clearColor().
You can also set the layer's fillMode to kCAFillModeForwards and set removedOnCompletion to false and that will have the layer preserve its "end of animation" state. But I personally would just set the strokeColor as outlined above, as using removedOnCompletion of true interferes with animationDidStop (see below).
Also, I might suggest that you also remove the layer once it's done with the animation so it doesn't continue to consume memory although it's no longer visible.
func shadowBall (x: CGFloat, y: CGFloat) {
let xpos: CGFloat = ((self.frame.width/2) + x)
let ypos: CGFloat = ((self.frame.height/2) + y)
let shadowBall = CAShapeLayer()
let shadowBalllRadius: CGFloat = 4
let shadowBallPath = UIBezierPath(ovalInRect: CGRect(x: xpos, y: ypos, width: CGFloat(shadowBalllRadius*2), height: CGFloat(shadowBalllRadius*2)))
shadowBall.path = shadowBallPath.CGPath
shadowBall.fillColor = UIColor.clearColor().CGColor
shadowBall.strokeColor = UIColor.clearColor().CGColor
shadowBall.lineWidth = 0.1
let animation = CABasicAnimation(keyPath: "strokeColor")
animation.fromValue = UIColor.whiteColor().CGColor
animation.toValue = UIColor.clearColor().CGColor
animation.duration = 1.0
animation.repeatCount = 0
animation.removedOnCompletion = true
animation.additive = false
animation.delegate = self
animation.setValue(shadowBall, forKey: "animationLayer")
self.layer.addSublayer(shadowBall)
shadowBall.addAnimation(animation, forKey: "strokeColor")
}
override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
if let layer = anim.valueForKey("animationLayer") as? CALayer {
layer.removeFromSuperlayer()
}
}
See How to remove a CALayer-object from animationDidStop?