How to remove a layer when its animation completes?

Question

I am making an iOS App. I have several CALayer objects that eventually will be deleted by a (shrinking) animation. When the animatio

Answer 1

It's been a long time since this question has been answered, however i'll try and add a more swifty solution, in case anybody is still looking for a more clean solution nowadays.

If everything you're interested in is simply remove the layer as soon as the CAAnimation is finished, you can assign the animation's delegate to a simple NSObject that holds a reference to the target layer and waits for the animation callback in order to dismiss it.

Let's call this helper object LayerRemover:

class LayerRemover: NSObject, CAAnimationDelegate {
    private weak var layer: CALayer?

    init(for layer: CALayer) {
        self.layer = layer
        super.init()
    }

    func animationDidStop(_ anim: CAAnimation, finished flag: Bool) {
        layer?.removeFromSuperlayer()
    }
}

Everything this object does is receiving a CALayer reference via initializer and waiting for the animationDidStop callback before removing the layer. At this point, as soon as the CAAnimation that's retaining it via the delegate property is deinitialized, the Layer remover gets purged too.

Now, all you have to do is actually instatiate this remover and use it:

let layer = CAShapeLayer()
layer.path = UIBezierPath(ovalIn: CGRect(x: 0, y: 0, width: 200, height: 100)).cgPath
let myAnimation = CABasicAnimation(keyPath: "strokeEnd")
...
myAnimation.delegate = LayerRemover(for: layer)

That's it!

Please note that you don't have to retain any reference to the LayerRemover object since from the Apple documentation we can read that

The delegate object is retained by the receiver. This is a rare exception to the memory management rules described in Advanced Memory Management Programming Guide.