Is there an way to pause an Core Animation and resume it at some time later?

Question

I have several Core Animation's going on at the same time. They all have an context and an animation id, where the context is the object that's beeing animated (UIImageView objects). I would like to pause them, so that the animation just stops temporarily, and then when some things are done, resume it to complete it. These things happen only on very fast scroll movements in an UIScrollView. I want to improve performance by stopping all ongoing animations but not the one that makes the scroll view scroll. I have implemented an custom animation of the contentOffset for that scroll view.

Answer 1

You can pause layer animations by setting the speed of the animation to zero, see How to pause the animation of a layer tree.

Answer 2

To anyone who comes searching, this is how you pause and resume animations:

https://developer.apple.com/library/archive/qa/qa1673/_index.html

Answer 3

The only way I have gotten around this is the following.

For each view you wish to stop animating:

Set the view's frame to the presentation layer

Remove all animations from that view

Perform your scroll

Recalculate animations

Add new animations to the view

I know it isn't what you want to hear, but it isn't as bad as it sounds. A good way to track the views you want to stop is to give them a predetermined tag.

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To remove animations:

[myView.layer removeAllAnimations]

[myView.layer removeAnimationForKey:@"theAnimationKey"]

Answer 4

The Core Animation Programming Guide has a section on Customizing the Timing of an Animation which includes a section on Pausing and Resuming Animations.