Open Radar

 
Summary:
In Xcode 8 with the iOS 10 SDK, if you attempt to animate a NSLayoutConstraint constant change (by calling `layoutIfNeeded`) alongside a `UIView` keyframe animation both from a `UIViewPropertyAnimator` with a spring timing curve, your app crashes.

Steps to Reproduce:
1. Create a `UIViewPropertyAnimator` with spring timing parameters
2. Create a view with a constraint to be animated
3. Change the constant of the constraint, add an animation block to the animator calling `layoutIfNeeded` on the appropriate view
4. Add another animation block to the animator where you attempt to use a keyframe animation
5. Start and pause the animator

Expected Results:
The animation is started and paused, and can happily be resumed

Actual Results:
The app crashes with `-[CAKeyframeAnimation setFromValue:]: unrecognized selector sent to instance`

Version:
iOS 10.3.1

Notes:
- Run the attached project to see the issue and a few workarounds
- This seems to be fixed in Xcode 9 beta 1 with the iOS 11 SDK
- You can work around this by:
  1. Not using a spring for the timing parameters
  2. Putting the `layoutIfNeeded` call in the keyframe animation as well
  3. Add an extension on `CAKeyframeAnimation` where you define a `fromValue` and ignore it being set