Screen flashes black when using custom animation controller to dismiss - ios

Question

I have written a custom animation controller to animate my view controller transition. Code as follows :
class PopupAnimationController: NSObject, UIViewControllerAnimatedTransitioning {
var backgroundColorView: UIView!
let duration: TimeInterval = 0.35
var dismiss = false
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return duration
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
if !dismiss {
animatePresentTransition(using: transitionContext)
} else {
animateDismissTransition(using: transitionContext)
}
}
func animatePresentTransition(using transitionContext: UIViewControllerContextTransitioning) {
guard let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
let toVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) else {
return
}
let containerView = transitionContext.containerView
let finalFrameForVC = transitionContext.finalFrame(for: toVC) // What is this about?
let bounds = UIScreen.main.bounds
let snapshotView = fromVC.view.snapshotView(afterScreenUpdates: false)
snapshotView?.frame = bounds
backgroundColorView = UIView(frame: bounds)
backgroundColorView.backgroundColor = UIColor.black.withAlphaComponent(0)
// Put the window at the bottom of the screen
toVC.view.frame = finalFrameForVC.offsetBy(dx: 0, dy: bounds.size.height)
// Layer out the views
containerView.addSubview(snapshotView!)
containerView.addSubview(backgroundColorView)
containerView.addSubview(toVC.view)
// The animation happens here
UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0, options: [], animations: {
self.backgroundColorView.backgroundColor = UIColor.black.withAlphaComponent(0.4)
toVC.view.frame = finalFrameForVC
}, completion: {
finished in
transitionContext.completeTransition(true)
})
}
func animateDismissTransition(using transitionContext: UIViewControllerContextTransitioning) {
guard let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) else {
return
}
UIView.animate(withDuration: duration, delay: 0, usingSpringWithDamping: 0.5, initialSpringVelocity: 0, options: [], animations: {
self.backgroundColorView.backgroundColor = UIColor.black.withAlphaComponent(0.0)
let bounds = UIScreen.main.bounds
fromVC.view.frame = fromVC.view.frame.offsetBy(dx: 0, dy: bounds.size.height)
}, completion: {
finished in
transitionContext.completeTransition(true)
})
}
}
I have implemented the UIViewControllerTransitioningDelegate methods in the controller that will use this transition like so :
extension PopupViewController: UIViewControllerTransitioningDelegate {
func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
transitionAnimator.dismiss = false
return transitionAnimator
}
func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
transitionAnimator.dismiss = true
return transitionAnimator
}
}
When I'm not using a spring in the animation (eg damping set to 1) it works perfectly. However if I include spring in the animation like in this example the screen flashes black when the controller is dismissed:
Not sure why this is happening. Any ideas on what I might be doing wrong where? Any pointers would be greatly appreciated!