UIViewPropertyAnimator cancels other animation - ios

Question

I have an animation made with UIViewPropertyAnimator. This animation shows or hide a view.
I have a switch button, and when I click on it, it will toggle the isShowingView and therefore show or hide the view.
But if for exemple, I hide the view while the "show" animation is still in progress, it cancels instantly the show animation, and the view just disappears without any animation.
Note that this doesn't happen with a simple UIView.animate instead of UIViewPropertyAnimator .
Here's some dummy code that replicates the issue :
var isShowingView = false
func onButtonClick() {
isShowingView.toggle()
refreshView()
}
func refreshView() {
let timing = UICubicTimingParameters(controlPoint1: CGPoint(x: 0.4, y: 0.0),
controlPoint2: CGPoint(x: 0.2, y: 1.0))
let animator = UIViewPropertyAnimator(duration: 0.3, timingParameters: timing)
animator.addAnimations {
self.myView.alpha = isShowingView ? 1 : 0
}
animator.addCompletion { position in
guard position == .end else { return }
if self.myView.alpha == 0.0 && isShowingView {
print("Bug here, at this moment the animation is broken <-----")
}
}
animator.startAnimation()
}
Is this the expected behavior? What could I do to prevent this?

Answer 1

As #matt said, the issue is that recreating a UIViewPropertyAnimator interrupts the current one.
The solution is to retain the property animator :
var isShowingView = false
let timing = UICubicTimingParameters(controlPoint1: CGPoint(x: 0.4, y: 0.0),
controlPoint2: CGPoint(x: 0.2, y: 1.0))
let animator = UIViewPropertyAnimator(duration: 0.3, timingParameters: timing)
func onButtonClick() {
isShowingView.toggle()
refreshView()
}
func refreshView() {
animator.addAnimations {
self.myView.alpha = isShowingView ? 1 : 0
}
animator.addCompletion { position in
guard position == .end else { return }
if self.myView.alpha == 0.0 && isShowingView {
print("Bug here, at this moment the animation is broken <-----")
}
}
animator.startAnimation()
}