addCoordinatedAnimations mangles scale transform animations

Since tvOS 9.2, the

addCoordinatedAnimations(-:completion:)

method of

UIFocusAnimationCoordinator

has exhibited a strange behavior. Assume you have a collection view whose cells use either affine or 3D scale transforms to scale-up their contents when focused:

override func didUpdateFocusInContext(context: UIFocusUpdateContext, withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
    coordinator.addCoordinatedAnimations({
        if self.focused {
            self.focusEffectsContainer.transform = CGAffineTransformMakeScale(1.158, 1.158)
        } else {
            self.focusEffectsContainer.transform = CGAffineTransformIdentity
        }
    }, completion: nil)
}

If you scroll through the collection view very quickly, cells that acquire and then immediately lose focus before being scrolled into the visible boundswill appear to be scaled-down for a few moments before returning to their identity transform states.

Check out a video of the bug here. You can also download the sample project here.

My best guess is that UIFocusAnimationCoordinator’s

addCoordinatedAnimations

method is using some unclamped animation parameters, which causes the return to an identity transform to over-downscale (like a bouncy animation). This, in conjunction with the (new since 9.2) delay applied to coordinated animations for offscreen views, might be causing the shrunken appearance of the cells awaiting the rest of their unfocusing animations.

I can “resolve” the issue by making nested UIView animation block calls from inside the

addCoordinatedAnimations

animation block argument, passing animation options that override the inherited curve and duration. But this results in sloppy looking animations all the time, even though it resolves the fast-scrolling transform edge case. I’d prefer to find a workaround that continues to use

addCoordinatedAnimations

the way it was intended.