CAShapeLayer and CABasicAnimation.


The problem is that there is no guarantee that the animationDidStop callback method will be called before the layer’s appearance is reset.

There are a couple of ways to fix this, the following way just involves adding some extra code without changing your existing code. 

CATransaction.setCompletionBlock {
    CATransaction.setDisableActions(true) // Fix code 1
    layer.fillColor = UIColor.red.cgColor // Changing color will flickering, if not set fix codes.
}

let animation = CABasicAnimation(keyPath: "path")
animation.isRemovedOnCompletion = false // Fix code 2
animation.fillMode = .forwards // Fix code 3