Black edges on return transition - swift

Question

I have implemented the following animated transition:
class PopInAndOutAnimator: NSObject, UIViewControllerAnimatedTransitioning {
fileprivate let _operationType : UINavigationControllerOperation
fileprivate let _transitionDuration : TimeInterval
init(operation: UINavigationControllerOperation) {
_operationType = operation
_transitionDuration = 0.4
}
init(operation: UINavigationControllerOperation, andDuration duration: TimeInterval) {
_operationType = operation
_transitionDuration = duration
}
//MARK: Push and Pop animations performers
internal func performPushTransition(_ transitionContext: UIViewControllerContextTransitioning) {
guard let toView = transitionContext.view(forKey: UITransitionContextViewKey.to) else {
// Something really bad happend and it is not possible to perform the transition
print("ERROR: Transition impossible to perform since either the destination view or the conteiner view are missing!")
return
}
let container = transitionContext.containerView
guard let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from) as? CollectionPushAndPoppable,
let fromView = fromViewController.collectionView,
let currentCell = fromViewController.sourceCell else {
// There are not enough info to perform the animation but it is still possible
// to perform the transition presenting the destination view
container.addSubview(toView)
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
return
}
// Add to container the destination view
container.addSubview(toView)
// Prepare the screenshot of the destination view for animation
let screenshotToView = UIImageView(image: toView.screenshot)
// set the frame of the screenshot equals to the cell's one
screenshotToView.frame = currentCell.frame
// Now I get the coordinates of screenshotToView inside the container
let containerCoord = fromView.convert(screenshotToView.frame.origin, to: container)
// set a new origin for the screenshotToView to overlap it to the cell
screenshotToView.frame.origin = containerCoord
// Prepare the screenshot of the source view for animation
let screenshotFromView = UIImageView(image: currentCell.screenshot)
screenshotFromView.frame = screenshotToView.frame
// Add screenshots to transition container to set-up the animation
container.addSubview(screenshotToView)
container.addSubview(screenshotFromView)
// Set views initial states
toView.isHidden = true
screenshotToView.isHidden = true
// Delay to guarantee smooth effects
let delayTime = DispatchTime.now() + Double(Int64(0.08 * Double(NSEC_PER_SEC))) / Double(NSEC_PER_SEC)
DispatchQueue.main.asyncAfter(deadline: delayTime) {
screenshotToView.isHidden = false
}
UIView.animate(withDuration: _transitionDuration, delay: 0, usingSpringWithDamping: 0, initialSpringVelocity: 0, options: [], animations: { () -> Void in
screenshotFromView.alpha = 0.0
screenshotToView.frame = UIScreen.main.bounds
screenshotToView.frame.origin = CGPoint(x: 0.0, y: 0.0)
screenshotFromView.frame = screenshotToView.frame
}) { _ in
screenshotToView.removeFromSuperview()
screenshotFromView.removeFromSuperview()
toView.isHidden = false
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
}
}
internal func performPopTransition(_ transitionContext: UIViewControllerContextTransitioning) {
guard let toView = transitionContext.view(forKey: UITransitionContextViewKey.to) else {
// Something really bad happend and it is not possible to perform the transition
print("ERROR: Transition impossible to perform since either the destination view or the conteiner view are missing!")
return
}
let container = transitionContext.containerView
guard let toViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to) as? CollectionPushAndPoppable,
let toCollectionView = toViewController.collectionView,
let fromViewController = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from),
let fromView = fromViewController.view,
let currentCell = toViewController.sourceCell else {
// There are not enough info to perform the animation but it is still possible
// to perform the transition presenting the destination view
container.addSubview(toView)
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
return
}
// Add destination view to the container view
container.addSubview(toView)
// Prepare the screenshot of the source view for animation
let screenshotFromView = UIImageView(image: fromView.screenshot)
screenshotFromView.frame = fromView.frame
// Prepare the screenshot of the destination view for animation
let screenshotToView = UIImageView(image: currentCell.screenshot)
screenshotToView.frame = screenshotFromView.frame
// Add screenshots to transition container to set-up the animation
container.addSubview(screenshotToView)
container.insertSubview(screenshotFromView, belowSubview: screenshotToView)
// Set views initial states
screenshotToView.alpha = 0.0
fromView.isHidden = true
currentCell.isHidden = true
let containerCoord = toCollectionView.convert(currentCell.frame.origin, to: container)
UIView.animate(withDuration: _transitionDuration, delay: 0, usingSpringWithDamping: 0.7, initialSpringVelocity: 0, options: [], animations: { () -> Void in
screenshotToView.alpha = 1.0
screenshotFromView.frame = currentCell.frame
screenshotFromView.frame.origin = containerCoord
screenshotToView.frame = screenshotFromView.frame
}) { _ in
currentCell.isHidden = false
screenshotFromView.removeFromSuperview()
screenshotToView.removeFromSuperview()
transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
}
}
//MARK: UIViewControllerAnimatedTransitioning
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return _transitionDuration
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
if _operationType == .push {
performPushTransition(transitionContext)
} else if _operationType == .pop {
performPopTransition(transitionContext)
}
}
}
The issue that I'm having is when my collection view cell returns. There is a small delay where the bottom of the cell has a black line. I'm not sure how to remove that delay or make that line white so that it isn't noticeable.

Answer 1

A quick hack is to set the background view color to white.