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

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 2

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 3

Only vertical dismiss

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:  view.frame.origin.x,
            y:  view.frame.origin.y + translation.y
        )
        panGesture.setTranslation(CGPoint.zero, in: self.view)
    } else if panGesture.state == .ended {
        let velocity = panGesture.velocity(in: view)
        if velocity.y >= 150 {
            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 4

Here is an extension I made based on @Wilson answer :

// MARK: IMPORT STATEMENTS
import UIKit

// MARK: EXTENSION
extension UIViewController {

    // MARK: IS SWIPABLE - FUNCTION
    func isSwipable() {
        let panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(handlePanGesture(_:)))
        self.view.addGestureRecognizer(panGestureRecognizer)
    }

    // MARK: HANDLE PAN GESTURE - FUNCTION
    @objc func handlePanGesture(_ panGesture: UIPanGestureRecognizer) {
        let translation = panGesture.translation(in: view)
        let minX = view.frame.width * 0.135
        var originalPosition = CGPoint.zero

        if panGesture.state == .began {
            originalPosition = view.center
        } else if panGesture.state == .changed {
            view.frame.origin = CGPoint(x: translation.x, y: 0.0)

            if panGesture.location(in: view).x > minX {
                view.frame.origin = originalPosition
            }

            if view.frame.origin.x <= 0.0 {
                view.frame.origin.x = 0.0
            }
        } else if panGesture.state == .ended {
            if view.frame.origin.x >= view.frame.width * 0.5 {
                UIView.animate(withDuration: 0.2
                     , animations: {
                        self.view.frame.origin = CGPoint(
                            x: self.view.frame.size.width,
                            y: self.view.frame.origin.y
                        )
                }, completion: { (isCompleted) in
                    if isCompleted {
                        self.dismiss(animated: false, completion: nil)
                    }
                })
            } else {
                UIView.animate(withDuration: 0.2, animations: {
                    self.view.frame.origin = originalPosition
                })
            }
        }
    }

}

USAGE

Inside your view controller you want to be swipable :

override func viewDidLoad() {
    super.viewDidLoad()

    self.isSwipable()
}

and it will be dismissible by swiping from the extreme left side of the view controller, as a navigation controller.

Answer 5

For those who really wanna dive a little deeper into Custom UIViewController Transition, I recommend this great tutorial from raywenderlich.com.

The original final sample project contains bug. So I fixed it and upload it to Github repo. The proj is in Swift 5, so you can easily run and play it.

Here is a preview:

And it's interactive too!

Happy hacking!

Answer 6

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!)
    }
}