Interactive Transition

gistfile1.swift

class ChromecastExpandedViewController: UIViewController {
    private var dismissInteractiveTransition = InteracitveTransition()

    override func viewDidLoad() {
          super.viewDidLoad()

          addPanGestureRecognizer()
    }
}

extension ChromecastExpandedViewController {
    override func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return dismissInteractiveTransition.hasStarted ? dismissInteractiveTransition : nil
    }
    
    private func addPanGestureRecognizer() {
        let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(dismissIfPanDownward(sender:)))
        panGestureRecognizer.maximumNumberOfTouches = 1
        view.addGestureRecognizer(panGestureRecognizer)
    }
    
    @objc private func dismissIfPanDownward(sender: UIPanGestureRecognizer) {
        let progressThreshold:CGFloat = 0.3
        let progress = dismissProgress(of: sender)
        
        switch sender.state {
        case .began:
            dismissInteractiveTransition.hasStarted = true
            dismiss(animated: true, completion: nil)
        case .changed:
            dismissInteractiveTransition.shouldFinish = progress > progressThreshold
            dismissInteractiveTransition.update(progress)
        case .cancelled:
            dismissInteractiveTransition.hasStarted = false
            dismissInteractiveTransition.cancel()
        case .ended:
            dismissInteractiveTransition.hasStarted = false
            dismissInteractiveTransition.shouldFinish
                ? dismissInteractiveTransition.finish()
                : dismissInteractiveTransition.cancel()
        default:
            break
        }
    }
    
    private func dismissProgress(of gestureRecognizer:UIPanGestureRecognizer) -> CGFloat {
        let touchPoint = gestureRecognizer.translation(in: gestureRecognizer.view)
        var downwardMovement = Float(touchPoint.y / view.bounds.height)
        downwardMovement = fmaxf(downwardMovement, 0.0)
        downwardMovement = fminf(downwardMovement, 1.0)
        let progress = CGFloat(downwardMovement)
        return progress
    }
}