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 to the original position?

For example, we can find this used on the Twitter app's photo views, or Snapchat's "discover" mode.

Similar threads point out that we can use a UISwipeGestureRecognizer and [self dismissViewControllerAnimated...] to dismiss a modal VC when a user swipes down. But this only handles a single swipe, not letting the user drag the modal around.

Answer 1

Swift 4.x, Using Pangesture

Simple way

Vertical

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

    @objc func onDrage(_ sender:UIPanGestureRecognizer) {
        let percentThreshold:CGFloat = 0.3
        let translation = sender.translation(in: view)

        let newX = ensureRange(value: view.frame.minX + translation.x, minimum: 0, maximum: view.frame.maxX)
        let progress = progressAlongAxis(newX, view.bounds.width)

        view.frame.origin.x = newX //Move view to new position

        if sender.state == .ended {
            let velocity = sender.velocity(in: view)
           if velocity.x >= 300 || progress > percentThreshold {
               self.dismiss(animated: true) //Perform dismiss
           } else {
               UIView.animate(withDuration: 0.2, animations: {
                   self.view.frame.origin.x = 0 // Revert animation
               })
          }
       }

       sender.setTranslation(.zero, in: view)
    }
}

Helper function

func progressAlongAxis(_ pointOnAxis: CGFloat, _ axisLength: CGFloat) -> CGFloat {
        let movementOnAxis = pointOnAxis / axisLength
        let positiveMovementOnAxis = fmaxf(Float(movementOnAxis), 0.0)
        let positiveMovementOnAxisPercent = fminf(positiveMovementOnAxis, 1.0)
        return CGFloat(positiveMovementOnAxisPercent)
    }

    func ensureRange<T>(value: T, minimum: T, maximum: T) -> T where T : Comparable {
        return min(max(value, minimum), maximum)
    }

Hard way

Refer this -> https://github.com/satishVekariya/DraggableViewController

Answer 2

I'll share how I did it in Swift 3 :

Result

Implementation

class MainViewController: UIViewController {

  @IBAction func click() {
    performSegue(withIdentifier: "showModalOne", sender: nil)
  }

}

---

class ModalOneViewController: ViewControllerPannable {
  override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = .yellow
  }

  @IBAction func click() {
    performSegue(withIdentifier: "showModalTwo", sender: nil)
  }
}

---

class ModalTwoViewController: ViewControllerPannable {
  override func viewDidLoad() {
    super.viewDidLoad()

    view.backgroundColor = .green
  }
}

Where the Modals View Controllers inherit from a class that I've built (ViewControllerPannable) to make them draggable and dismissible when reach certain velocity.

ViewControllerPannable class

class ViewControllerPannable: UIViewController {
  var panGestureRecognizer: UIPanGestureRecognizer?
  var originalPosition: CGPoint?
  var currentPositionTouched: CGPoint?

  override func viewDidLoad() {
    super.viewDidLoad()

    panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(panGestureAction(_:)))
    view.addGestureRecognizer(panGestureRecognizer!)
  }

  func panGestureAction(_ panGesture: UIPanGestureRecognizer) {
    let translation = panGesture.translation(in: view)

    if panGesture.state == .began {
      originalPosition = view.center
      currentPositionTouched = panGesture.location(in: view)
    } else if panGesture.state == .changed {
        view.frame.origin = CGPoint(
          x: translation.x,
          y: translation.y
        )
    } else if panGesture.state == .ended {
      let velocity = panGesture.velocity(in: view)

      if velocity.y >= 1500 {
        UIView.animate(withDuration: 0.2
          , animations: {
            self.view.frame.origin = CGPoint(
              x: self.view.frame.origin.x,
              y: self.view.frame.size.height
            )
          }, completion: { (isCompleted) in
            if isCompleted {
              self.dismiss(animated: false, completion: nil)
            }
        })
      } else {
        UIView.animate(withDuration: 0.2, animations: {
          self.view.center = self.originalPosition!
        })
      }
    }
  }
}

Answer 3

In Objective C : Here's the code

inviewDidLoad

UISwipeGestureRecognizer *swipeRecognizer = [[UISwipeGestureRecognizer alloc]
                                             initWithTarget:self action:@selector(swipeDown:)];
swipeRecognizer.direction = UISwipeGestureRecognizerDirectionDown;
[self.view addGestureRecognizer:swipeRecognizer];

//Swipe Down Method

- (void)swipeDown:(UIGestureRecognizer *)sender{
[self dismissViewControllerAnimated:YES completion:nil];
}

Answer 4

Massively updates the repo for Swift 4.

For Swift 3, I have created the following to present a UIViewController from right to left and dismiss it by pan gesture. I have uploaded this as a GitHub repository.

DismissOnPanGesture.swift file:

//  Created by David Seek on 11/21/16.
//  Copyright © 2016 David Seek. All rights reserved.

import UIKit

class DismissAnimator : NSObject {
}

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

    func animateTransition(using transitionContext: UIViewControllerContextTransitioning) {

        let screenBounds = UIScreen.main.bounds
        let fromVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.from)
        let toVC = transitionContext.viewController(forKey: UITransitionContextViewControllerKey.to)
        var x:CGFloat      = toVC!.view.bounds.origin.x - screenBounds.width
        let y:CGFloat      = toVC!.view.bounds.origin.y
        let width:CGFloat  = toVC!.view.bounds.width
        let height:CGFloat = toVC!.view.bounds.height
        var frame:CGRect   = CGRect(x: x, y: y, width: width, height: height)

        toVC?.view.alpha = 0.2

        toVC?.view.frame = frame
        let containerView = transitionContext.containerView

        containerView.insertSubview(toVC!.view, belowSubview: fromVC!.view)


        let bottomLeftCorner = CGPoint(x: screenBounds.width, y: 0)
        let finalFrame = CGRect(origin: bottomLeftCorner, size: screenBounds.size)

        UIView.animate(
            withDuration: transitionDuration(using: transitionContext),
            animations: {
                fromVC!.view.frame = finalFrame
                toVC?.view.alpha = 1

                x = toVC!.view.bounds.origin.x
                frame = CGRect(x: x, y: y, width: width, height: height)

                toVC?.view.frame = frame
            },
            completion: { _ in
                transitionContext.completeTransition(!transitionContext.transitionWasCancelled)
            }
        )
    }
}

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

let transition: CATransition = CATransition()

func presentVCRightToLeft(_ fromVC: UIViewController, _ toVC: UIViewController) {
    transition.duration = 0.5
    transition.type = kCATransitionPush
    transition.subtype = kCATransitionFromRight
    fromVC.view.window!.layer.add(transition, forKey: kCATransition)
    fromVC.present(toVC, animated: false, completion: nil)
}

func dismissVCLeftToRight(_ vc: UIViewController) {
    transition.duration = 0.5
    transition.timingFunction = CAMediaTimingFunction(name: kCAMediaTimingFunctionEaseInEaseOut)
    transition.type = kCATransitionPush
    transition.subtype = kCATransitionFromLeft
    vc.view.window!.layer.add(transition, forKey: nil)
    vc.dismiss(animated: false, completion: nil)
}

func instantiatePanGestureRecognizer(_ vc: UIViewController, _ selector: Selector) {
    var edgeRecognizer: UIScreenEdgePanGestureRecognizer!
    edgeRecognizer = UIScreenEdgePanGestureRecognizer(target: vc, action: selector)
    edgeRecognizer.edges = .left
    vc.view.addGestureRecognizer(edgeRecognizer)
}

func dismissVCOnPanGesture(_ vc: UIViewController, _ sender: UIScreenEdgePanGestureRecognizer, _ interactor: Interactor) {
    let percentThreshold:CGFloat = 0.3
    let translation = sender.translation(in: vc.view)
    let fingerMovement = translation.x / vc.view.bounds.width
    let rightMovement = fmaxf(Float(fingerMovement), 0.0)
    let rightMovementPercent = fminf(rightMovement, 1.0)
    let progress = CGFloat(rightMovementPercent)

    switch sender.state {
    case .began:
        interactor.hasStarted = true
        vc.dismiss(animated: true, completion: nil)
    case .changed:
        interactor.shouldFinish = progress > percentThreshold
        interactor.update(progress)
    case .cancelled:
        interactor.hasStarted = false
        interactor.cancel()
    case .ended:
        interactor.hasStarted = false
        interactor.shouldFinish
            ? interactor.finish()
            : interactor.cancel()
    default:
        break
    }
}

Easy usage:

import UIKit

class VC1: UIViewController, UIViewControllerTransitioningDelegate {

    let interactor = Interactor()

    @IBAction func present(_ sender: Any) {
        let vc = self.storyboard?.instantiateViewController(withIdentifier: "VC2") as! VC2
        vc.transitioningDelegate = self
        vc.interactor = interactor

        presentVCRightToLeft(self, vc)
    }

    func animationController(forDismissed dismissed: UIViewController) -> UIViewControllerAnimatedTransitioning? {
        return DismissAnimator()
    }

    func interactionControllerForDismissal(using animator: UIViewControllerAnimatedTransitioning) -> UIViewControllerInteractiveTransitioning? {
        return interactor.hasStarted ? interactor : nil
    }
}

class VC2: UIViewController {

    var interactor:Interactor? = nil

    override func viewDidLoad() {
        super.viewDidLoad()
        instantiatePanGestureRecognizer(self, #selector(gesture))
    }

    @IBAction func dismiss(_ sender: Any) {
        dismissVCLeftToRight(self)
    }

    func gesture(_ sender: UIScreenEdgePanGestureRecognizer) {
        dismissVCOnPanGesture(self, sender, interactor!)
    }
}

Answer 5

I've created an easy to use extension.

Just inherent Your UIViewController with InteractiveViewController and you are done InteractiveViewController

call method showInteractive() from your controller to show as Interactive.

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
        }
    }

}