Test whether a UIView is in the middle of animation

Question

A UIView has a layer (CALayer). You can send animationKeys to it, which will give you an array of keys which identify the animations attached to the layer. I suppose that if there are any entries, the animation(s) are running. If you want to dig even deeper have a look at the CAMediaTiming protocol which CALayer adopts. It does some more information on the current animation.

Important: If you add an animation with a nil key ([layer addAnimation:animation forKey:nil]), animationKeys returns nil.

iOS 9+ method, works even when layer.animationKeys contains no keys:

let isInTheMiddleOfAnimation = UIView.inheritedAnimationDuration > 0

From the docs:

This method only returns a non-zero value if called within a UIView animation block.

Animations are attached in fact to the underlying Core Animation CALayer class

So I think you can just check myView.layer.animationKeys

I'm not sure of the context of the question but I had was attempting to find out if a view was animating before starting a second animation to avoid skipping. However there is a UIView animation option UIViewAnimationOptionBeginFromCurrentState that will combine the animations if necessary to give a smooth appearance. Thereby eliminating my need to know if the view was animating.

There are a lot of out-of-date answers here. I just needed to prevent a UIView animation being started if there was one running on the same view, so I created a category on UIView:-

extension UIView {

    var isAnimating: Bool {
        return (self.layer.animationKeys()?.count ?? 0) > 0
    }

}

This way I can just check any view's animation status like this:-

if !myView.isAnimating {
  UIView.animate(withDuration: 0.4) {
    ...
  }
} else {
  // already animating
}

This seems less fragile than keeping track of it with a state variable.

There is a hitch with the animationKeys trick.

Sometimes there could be a few animationKeys lingering after an animation is completed.

This means that a non-animating layer could return a set of animationKeys even if it isn't actually animating.

You can make sure that animationKeys are automatically removed by setting an animation's removedOnCompletion property to YES.

e.g.

CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"aPath"];
animation.removedOnCompletion = YES;

If you do this for all the animations you apply to your layer, it will ensure that when the layer isn't animating there are no animationKeys present.