Test whether a UIView is in the middle of animatio

问题:

Is there any way to tell if a UIView is in the middle of an animation? When I print out the view object while it is moving I notice that there is an "animations" entry:

search bar should end editing: <UISearchBar: 0x2e6240; frame = (0 0; 320 88); text = ''; autoresize = W+BM; animations = { position=<CABasicAnimation: 0x6a69c40>; bounds=<CABasicAnimation: 0x6a6d4d0>; }; layer = <CALayer: 0x2e6e00>>

When the animation has stopped and I print the view, the "animations" entry is now gone:

search bar should end editing: <UISearchBar: 0x2e6240; frame = (0 0; 320 88); text = ''; autoresize = W+BM; layer = <CALayer: 0x2e6e00>>

回答1:

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.

回答2:

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

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

回答3:

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.

回答4:

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.

回答5:

Some of these didn't work for me. The reason for that is that these animations are asynchronous.

What I did is defined a property

@property BOOL viewIsAnimating;

And in my animation

[UIView animateWithDuration:0.25
                 animations:^{
                     viewIsAnimating = YES;
                 } completion:^(BOOL finished) {
                     if (finished) {
                         viewIsAnimating = NO;
                     }
                 }];

回答6:

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.

回答7:

Ref to the question: UIView center position during animation

I compare the view's frame and layer.presentation()?.frame to check it is animating. If leftView is on the way to finish, the leftView.layer.presentation()?.frame does not equal to its frame:

if self.leftView.layer.presentation()?.frame == self.leftView.frame {
   // the animation finished
} else {
   // the animation on the way
}

But this method may not work if the view move to the end position during the animation. More condition check may be necessary.

回答8:

You could query the presentation layer as suggested here My presentation layer does not match my model layer even though I have no animations