In past apps, I tended to have one UIDynamicAnimator in my ViewController and that was that. UIDynamicAnimator allows you to use UIDynamics / effects on your UIViews.
The issue that I ran into was that removeBehavior(_:), which “Removes a specified dynamic behavior from a dynamic animator“, didn’t seem to work. I would keep track of specific UIDynamicBehavior instances and pass them as the argument for removeBehavior(_:) but it didn’t appear to remove the behavior.
What does work is calling removeAllBehaviors() on the UIDynamicAnimator. This is fine if you only have one UIView. But most likely, you have multiple UIViews & behaviors. Calling remove all on the only animator isn’t a good idea. That could leave UIViews frozen out of place.
Recently, I released a fun weekend app, Fun Faces. Browsing stack overflow, it occurred to me to use multiple UIDynamicAnimators. One for each UIView I wanted to animate. This worked for my use case, where calling removeAllBehaviors() doesn’t interrupt the other UIView’s behaviors (if any).
Using multiple UIDynamicAnimators isn’t an answer if you have multiple UIViews under the same animator with UICollisionBehavior or other effects that let the UIViews interact with each other.