Animate CAShapeLayer path on animated bounds change

I know this is an old question but I can provide you a solution which appears similar to Mr Lockwoods approach. Sadly the source code here is swift so you will need to convert it to ObjC.

As mentioned before if the layer is a backing layer for a view you can intercept the CAAction’s in the view itself. This however isn’t convenient for example if the backing layer is used in more then one view.

The good news is actionForLayer:forKey: actually calls actionForKey: in the backing layer.

It’s in the actionForKey: in the backing layer where we can intercept these calls and provide an animation for when the path is changed.

An example layer written in swift is as follows:

class AnimatedBackingLayer: CAShapeLayer
{

    override var bounds: CGRect
    {
        didSet
        {
            if !CGRectIsEmpty(bounds)
            {
                path = UIBezierPath(roundedRect: CGRectInset(bounds, 10, 10), cornerRadius: 5).CGPath
            }
        }
    }

    override func actionForKey(event: String) -> CAAction?
    {
        if event == "path"
        {
            if let action = super.actionForKey("backgroundColor") as? CABasicAnimation
            {
                let animation = CABasicAnimation(keyPath: event)
                animation.fromValue = path
                // Copy values from existing action
                animation.autoreverses = action.autoreverses
                animation.beginTime = action.beginTime
                animation.delegate = action.delegate
                animation.duration = action.duration
                animation.fillMode = action.fillMode
                animation.repeatCount = action.repeatCount
                animation.repeatDuration = action.repeatDuration
                animation.speed = action.speed
                animation.timingFunction = action.timingFunction
                animation.timeOffset = action.timeOffset
                return animation
            }
        }
        return super.actionForKey(event)
    }

}