CABasicAnimation Quickly Jumping Before Animation Start - ios

Question

I have a CABasicAnimation animating the strokeEnd property of a CAShapeLayer. Every time I add the animation, it quickly jumps through the animation and then goes and does the real animation (as seen in the image above). If I add the animation in the viewDidLoad, this doesn't happen.
Here's my animation code:
let progressAnim = CABasicAnimation(keyPath: "strokeEnd")
progressAnim.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionDefault)
progressAnim.duration = 4.5
progressAnim.fromValue = 0.0
progressAnim.toValue = 1.0
progressAnim.removedOnCompletion = false
progressLayer.addAnimation(progressAnim, forKey: "progressAnimation")
progressLayer.strokeEnd = 1.0
I'm not sure what exactly I'm doing wrong, any help would be highly appreciated. Thanks!

Answer 1

My problem was with the line progressLayer.strokeEnd = 1.0. The reason I had that in my code was to stop the animation from going back to it's original values when it finished animating.
The next solution would be to set the fillMode to progressAnim.fillMode = kCAFillModeForwards and removedOnCompletion to progressAnim.removedOnCompletion = false. This sort of fixed my problem. But it created another. In my code, this solution doesn't update the strokeEnd property to the toValue.
My final solution was to set the toValue to the strokeEnd inside override func animationDidStop(anim: CAAnimation, finished flag: Bool).
My animation code:
let progressAnim = CABasicAnimation(keyPath: "strokeEnd")
progressAnim.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionDefault)
progressAnim.duration = animationDuration
progressAnim.fromValue = 0.0
progressAnim.toValue = 0.5
progressAnim.delegate = self
progressLayer.addAnimation(progressAnim, forKey: "progressAnimation")
Code for when animation is complete:
override func animationDidStop(anim: CAAnimation, finished flag: Bool) {
progressLayer.strokeEnd = 0.5
progressLayer.removeAllAnimations()
}