Swift interactive transition - view from second view controller is flashing when cancelling the transition

Question

i´m trying to make my own interactive transition in swift. In my sample project I have two view controllers. With my own transition I can swipe to each other. My problem is: when swiping from the first to the second view controller the second (where I want to swipe in) view controller is appears for a millisecond on the screen, when I did cancel the transition in my pan gesture.

I tried to solve the problem by taking a snapshot from the first view controller and lay it on the transition layer when the transition cancelled. That worked on my iPhone 8, but on the iPhone XS I get the same flash for a millisecond.

The flashing only appears when I swipe very fast over the screen.

Anyone with the same problem.

PangestureHandler:

@IBAction func HandlePan(_ sender: UIPanGestureRecognizer) {
    let percentThreshold:CGFloat = 0.25

    let translation = sender.translation(in: view)
    var verticalMovement = (translation.y) / view.bounds.height
    verticalMovement = verticalMovement - verticalMovement - verticalMovement
    let downwardMovement = fmaxf(Float(verticalMovement), 0.0)
    let downwardMovementPercent = fminf(downwardMovement, 1.0)
    let progress = CGFloat(downwardMovementPercent)

    let movementToStart: CGFloat = 0.0

    let interactor = self.interactor

    switch sender.state {
    case .began:
        print(".began")
    case .changed:
        print("progress: \(progress)")
        if progress > movementToStart && !interactor.hasStarted {
            interactor.hasStarted = true
            performSegue(withIdentifier: "segueToSecondVC", sender: nil)
            interactor.update(progress - movementToStart)
        }
        if interactor.hasStarted {
            interactor.update(progress - movementToStart)
            interactor.shouldFinish = progress > percentThreshold
        }
    case .cancelled:
        print("cancel")
        interactor.hasStarted = false
        interactor.cancel()
    case .ended:
        interactor.hasStarted = false
        if interactor.shouldFinish {
            interactor.finish()
        } else {
            interactor.cancel()
            print("interactor cancel")
        }

    default:
        break
    }
}

AnimatorClass:

import UIKit

class PresentAnimator: NSObject, UIViewControllerAnimatedTransitioning {




private var myView: UIView!

func transitionDuration(using transitionContext: UIViewControllerContextTransitioning?) -> TimeInterval {
    return 0.6

}


func animationEnded(_ transitionCompleted: Bool) {
    if !transitionCompleted {
        self.myView.alpha = 1.0
    }
}

func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {
    guard let fromVC = transitionContext.viewController(forKey: .from), let toVC = transitionContext.viewController(forKey: .to) else { return }
    let containerView = transitionContext.containerView


    let screenBounds = UIScreen.main.bounds
    let startPoint = CGPoint(x: 0, y: UIScreen.main.bounds.height )
    toVC.view.frame = CGRect(origin: startPoint, size: screenBounds.size)
    toVC.view.clipsToBounds = true

    self.myView = fromVC.view.snapshotView(afterScreenUpdates: false)
    containerView.addSubview(myView)
    self.myView.alpha = 0.0

    containerView.insertSubview(toVC.view, aboveSubview: fromVC.view)

    let bottomLeftCorner = CGPoint(x: 0, y: 0)
    let finalFrame = CGRect(origin: bottomLeftCorner, size: screenBounds.size)
    let duration = transitionDuration(using: transitionContext)



    UIView.animate(
        withDuration: duration, delay: 10.0, options: .curveLinear,
        animations: {
            toVC.view.frame = finalFrame
            self.myView.removeFromSuperview()
    },
        completion: { _ in
            self.myView.removeFromSuperview()
            transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
    })

}

}