Written by Paul Hudson @twostraws
Spring animations work by changing from a start state to an end state, with a slight overshoot and bounce at the end. For example, if you want to animate a view moving from X:0 to X:100, it might move to X:120 before bouncing back to X:80, then X:110 and finally X:100, as if the animation were attached to a spring.
Spring animations are built into iOS as of iOS 7.0 and require two values: how "springy" the spring should be, and how fast it should start. The first value is specified with usingSpringWithDamping, where higher values make the bouncing finish faster. The second value is specified with initialSpringVelocity, where higher values give the spring more initial momentum.
Here's the code to make a view fade out, then fade it the tiniest bit, then fade out again – all done using a spring animation:
UIView.animate(withDuration: 1, delay: 1, usingSpringWithDamping: 0.5, initialSpringVelocity: 5, options: .curveEaseInOut, animations: {
self.viewToAnimate.alpha = 0
}) { _ in
self.viewToAnimate.removeFromSuperview()
}Available from iOS 7.0
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