The UIViewControllerContextTransitioning won't give me a ViewController - ios

Question

I am facing an incomprehensible problem I have a CollectionViewController and I want to make a custom animation.
My collection is a gallery and I want to switch from collection gallery. to fullscreen gallery.
So I have ControllerTransitionDelegate
extension NavigationGalleryViewController: UIViewControllerTransitioningDelegate {
func presentationController(forPresented presented: UIViewController, presenting: UIViewController?, source: UIViewController) -> UIPresentationController? {
return DimmingPresentationController(presentedViewController: presented, presenting: presenting)
}
func animationController(forPresented presented: UIViewController, presenting: UIViewController, source: UIViewController) -> UIViewControllerAnimatedTransitioning? {
guard let selectedCellFrame = self.collectionView?.cellForItem(at: IndexPath(item: index, section: 0))?.frame else { return nil }
return PresentingAnimator(pageIndex: index, originFrame: selectedCellFrame)
}
My DimmingPresentationController
class DimmingPresentationController: UIPresentationController {
lazy var background = UIView(frame: .zero)
override var shouldRemovePresentersView: Bool {
return false
}
override func presentationTransitionWillBegin() {
setupBackground()
// Grabing the coordinator responsible for the presentation so that the background can be animated at the same rate
if let coordinator = presentedViewController.transitionCoordinator {
coordinator.animate(alongsideTransition: { (_) in
self.background.alpha = 1
}, completion: nil)
}
}
private func setupBackground() {
background.backgroundColor = UIColor.black
background.autoresizingMask = [.flexibleWidth, .flexibleHeight]
background.frame = containerView!.bounds
containerView!.insertSubview(background, at: 0)
background.alpha = 0
}
}
And my presenting animator
class PresentingAnimator: NSObject, UIViewControllerAnimatedTransitioning {
private let indexPath: IndexPath
private let originFrame: CGRect
private let duration: TimeInterval = 0.5
init(pageIndex: Int, originFrame: CGRect) {
self.indexPath = IndexPath(item: pageIndex, section: 0)
self.originFrame = originFrame
super.init()
}
func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
return duration
}
func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
guard let toView = transitionContext.view(forKey: .to),
let fromVC = transitionContext.viewController(forKey: .from) as? NavigationGalleryViewController, // The problem is here !
let fromView = fromVC.collectionView?.cellForItem(at: indexPath) as? InstallationViewCell
else {
transitionContext.completeTransition(true)
return
}
// All the animation things
}
My BIG problem is that my execution go inside the else because he can't find the FromVC from the transitionContext.viewController.
And here is how I call my Gallery
gallery = SwiftPhotoGallery(delegate: self, dataSource: self)
// Gallery visual colours stuff
gallery.modalPresentationStyle = .custom
gallery.transitioningDelegate = self
present(gallery, animated: true, completion: { () -> Void in
self.gallery.currentPage = self.index
})
}
This is what I receive from the transitionContext :
Why the transitionContext won't give me the right VC ?

Answer 1

Well, I checked and noticed that transitionContext.viewController(forKey: .from) is NavigationController.
In line: let fromVC = transitionContext.viewController(forKey: .from) as? NavigationGalleryViewController should be nil, because it is not NavigationGalleryViewController but NavigationController.
If you want you can make smth like this: let fromVC = transitionContext.viewController(forKey: .from).childViewControllers.first as? NavigationGalleryViewController