In iOS, how to drag down to dismiss a modal?

Question

A common way to dismiss a modal is to swipe down - How do we allows the user to drag the modal down, if it\'s far enough, the modal\'s dismissed, otherwise it animates back

Answer 1

This my simple class for Drag ViewController from axis. Just herited your class from DraggableViewController.

MyCustomClass: DraggableViewController

Work only for presented ViewController.

// MARK: - DraggableViewController

public class DraggableViewController: UIViewController {

    public let percentThresholdDismiss: CGFloat = 0.3
    public var velocityDismiss: CGFloat = 300
    public var axis: NSLayoutConstraint.Axis = .horizontal
    public var backgroundDismissColor: UIColor = .black {
        didSet {
            navigationController?.view.backgroundColor = backgroundDismissColor
        }
    }

    // MARK: LifeCycle

    override func viewDidLoad() {
        super.viewDidLoad()
        view.addGestureRecognizer(UIPanGestureRecognizer(target: self, action: #selector(onDrag(_:))))
    }

    // MARK: Private methods

    @objc fileprivate func onDrag(_ sender: UIPanGestureRecognizer) {

        let translation = sender.translation(in: view)

        // Movement indication index
        let movementOnAxis: CGFloat

        // Move view to new position
        switch axis {
        case .vertical:
            let newY = min(max(view.frame.minY + translation.y, 0), view.frame.maxY)
            movementOnAxis = newY / view.bounds.height
            view.frame.origin.y = newY

        case .horizontal:
            let newX = min(max(view.frame.minX + translation.x, 0), view.frame.maxX)
            movementOnAxis = newX / view.bounds.width
            view.frame.origin.x = newX
        }

        let positiveMovementOnAxis = fmaxf(Float(movementOnAxis), 0.0)
        let positiveMovementOnAxisPercent = fminf(positiveMovementOnAxis, 1.0)
        let progress = CGFloat(positiveMovementOnAxisPercent)
        navigationController?.view.backgroundColor = UIColor.black.withAlphaComponent(1 - progress)

        switch sender.state {
        case .ended where sender.velocity(in: view).y >= velocityDismiss || progress > percentThresholdDismiss:
            // After animate, user made the conditions to leave
            UIView.animate(withDuration: 0.2, animations: {
                switch self.axis {
                case .vertical:
                    self.view.frame.origin.y = self.view.bounds.height

                case .horizontal:
                    self.view.frame.origin.x = self.view.bounds.width
                }
                self.navigationController?.view.backgroundColor = UIColor.black.withAlphaComponent(0)

            }, completion: { finish in
                self.dismiss(animated: true) //Perform dismiss
            })
        case .ended:
            // Revert animation
            UIView.animate(withDuration: 0.2, animations: {
                switch self.axis {
                case .vertical:
                    self.view.frame.origin.y = 0

                case .horizontal:
                    self.view.frame.origin.x = 0
                }
            })
        default:
            break
        }
        sender.setTranslation(.zero, in: view)
    }
}

Answer 2

I figured out super simple way to do this. Just put the following code into your view controller:

Swift 4

override func viewDidLoad() {
    super.viewDidLoad()
    let gestureRecognizer = UIPanGestureRecognizer(target: self,
                                                   action: #selector(panGestureRecognizerHandler(_:)))
    view.addGestureRecognizer(gestureRecognizer)
}

@IBAction func panGestureRecognizerHandler(_ sender: UIPanGestureRecognizer) {
    let touchPoint = sender.location(in: view?.window)
    var initialTouchPoint = CGPoint.zero

    switch sender.state {
    case .began:
        initialTouchPoint = touchPoint
    case .changed:
        if touchPoint.y > initialTouchPoint.y {
            view.frame.origin.y = touchPoint.y - initialTouchPoint.y
        }
    case .ended, .cancelled:
        if touchPoint.y - initialTouchPoint.y > 200 {
            dismiss(animated: true, completion: nil)
        } else {
            UIView.animate(withDuration: 0.2, animations: {
                self.view.frame = CGRect(x: 0,
                                         y: 0,
                                         width: self.view.frame.size.width,
                                         height: self.view.frame.size.height)
            })
        }
    case .failed, .possible:
        break
    }
}

Answer 3

Here is a one-file solution based on @wilson's answer (thanks

Answer 4

What you're describing is an interactive custom transition animation. You are customizing both the animation and the driving gesture of a transition, i.e. the dismissal (or not) of a presented view controller. The easiest way to implement it is by combining a UIPanGestureRecognizer with a UIPercentDrivenInteractiveTransition.

My book explains how to do this, and I have posted examples (from the book). This particular example is a different situation - the transition is sideways, not down, and it is for a tab bar controller, not a presented controller - but the basic idea is exactly the same:

https://github.com/mattneub/Programming-iOS-Book-Examples/blob/master/bk2ch06p296customAnimation2/ch19p620customAnimation1/AppDelegate.swift

If you download that project and run it, you will see that what is happening is exactly what you are describing, except that it is sideways: if the drag is more than half, we transition, but if not, we cancel and snap back into place.

Answer 5

You can use a UIPanGestureRecognizer to detect the user's drag and move the modal view with it. If the ending position is far enough down, the view can be dismissed, or otherwise animated back to its original position.

Check out this answer for more information on how to implement something like this.

Answer 6

I just created a tutorial for interactively dragging down a modal to dismiss it.

http://www.thorntech.com/2016/02/ios-tutorial-close-modal-dragging/

I found this topic to be confusing at first, so the tutorial builds this out step-by-step.

If you just want to run the code yourself, this is the repo:

https://github.com/ThornTechPublic/InteractiveModal

This is the approach I used:

View Controller

You override the dismiss animation with a custom one. If the user is dragging the modal, the interactor kicks in.

import UIKit

class ViewController: UIViewController {
    let interactor = Interactor()
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if let destinationViewController = segue.destinationViewController as? ModalViewController {
            destinationViewController.transitioningDelegate = self
            destinationViewController.interactor = interactor
        }
    }
}

extension ViewController: UIViewControllerTransitioningDelegate {
    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return DismissAnimator()
    }
    func interactionControllerForDismissal(animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactor.hasStarted ? interactor : nil
    }
}

Dismiss Animator

You create a custom animator. This is a custom animation that you package inside a UIViewControllerAnimatedTransitioning protocol.

import UIKit

class DismissAnimator : NSObject {
}

extension DismissAnimator : UIViewControllerAnimatedTransitioning {
    func transitionDuration(transitionContext: UIViewControllerContextTransitioning?) -> NSTimeInterval {
        return 0.6
    }

    func animateTransition(transitionContext: UIViewControllerContextTransitioning) {
        guard
            let fromVC = transitionContext.viewControllerForKey(UITransitionContextFromViewControllerKey),
            let toVC = transitionContext.viewControllerForKey(UITransitionContextToViewControllerKey),
            let containerView = transitionContext.containerView()
            else {
                return
        }
        containerView.insertSubview(toVC.view, belowSubview: fromVC.view)
        let screenBounds = UIScreen.mainScreen().bounds
        let bottomLeftCorner = CGPoint(x: 0, y: screenBounds.height)
        let finalFrame = CGRect(origin: bottomLeftCorner, size: screenBounds.size)

        UIView.animateWithDuration(
            transitionDuration(transitionContext),
            animations: {
                fromVC.view.frame = finalFrame
            },
            completion: { _ in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled())
            }
        )
    }
}

Interactor

You subclass UIPercentDrivenInteractiveTransition so that it can act as your state machine. Since the interactor object is accessed by both VCs, use it to keep track of the panning progress.

import UIKit

class Interactor: UIPercentDrivenInteractiveTransition {
    var hasStarted = false
    var shouldFinish = false
}

Modal View Controller

This maps the pan gesture state to interactor method calls. The translationInView() y value determines whether the user crossed a threshold. When the pan gesture is .Ended, the interactor either finishes or cancels.

import UIKit

class ModalViewController: UIViewController {

    var interactor:Interactor? = nil

    @IBAction func close(sender: UIButton) {
        dismissViewControllerAnimated(true, completion: nil)
    }

    @IBAction func handleGesture(sender: UIPanGestureRecognizer) {
        let percentThreshold:CGFloat = 0.3

        // convert y-position to downward pull progress (percentage)
        let translation = sender.translationInView(view)
        let verticalMovement = translation.y / view.bounds.height
        let downwardMovement = fmaxf(Float(verticalMovement), 0.0)
        let downwardMovementPercent = fminf(downwardMovement, 1.0)
        let progress = CGFloat(downwardMovementPercent)
        guard let interactor = interactor else { return }

        switch sender.state {
        case .Began:
            interactor.hasStarted = true
            dismissViewControllerAnimated(true, completion: nil)
        case .Changed:
            interactor.shouldFinish = progress > percentThreshold
            interactor.updateInteractiveTransition(progress)
        case .Cancelled:
            interactor.hasStarted = false
            interactor.cancelInteractiveTransition()
        case .Ended:
            interactor.hasStarted = false
            interactor.shouldFinish
                ? interactor.finishInteractiveTransition()
                : interactor.cancelInteractiveTransition()
        default:
            break
        }
    }

}