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

由 六月ゝ 毕业季﹏ 提交于 2019-12-17 05:16:06

问题


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.


回答1:


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
        }
    }

}



回答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!
        })
      }
    }
  }
}



回答3:


created a demo for interactively dragging down to dismiss view controller like snapchat's discover mode. Check this github for sample project.




回答4:


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




回答5:


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
    }
}



回答6:


Here is a one-file solution based on @wilson's answer (thanks 👍 ) with the following improvements:

List of Improvements from previous solution

  • Limit panning so that the view only goes down:
    • Avoid horizontal translation by only updating the y coordinate of view.frame.origin
    • Avoid panning out of the screen when swiping up with let y = max(0, translation.y)
  • Also dismiss the view controller based on where the finger is released (defaults to the bottom half of the screen) and not just based on the velocity of the swipe
  • Show view controller as modal to ensure the previous viewcontroller appears behind and avoid a black background (should answer your question @nguyễn-anh-việt)
  • Remove unneeded currentPositionTouched and originalPosition
  • Expose the following parameters:
    • minimumVelocityToHide: what speed is enough to hide (defaults to 1500)
    • minimumScreenRatioToHide: how low is enough to hide (defaults to 0.5)
    • animationDuration : how fast do we hide/show (defaults to 0.2s)

Solution

Swift 3 & Swift 4 :

//
//  PannableViewController.swift
//

import UIKit

class PannableViewController: UIViewController {
    public var minimumVelocityToHide: CGFloat = 1500
    public var minimumScreenRatioToHide: CGFloat = 0.5
    public var animationDuration: TimeInterval = 0.2

    override func viewDidLoad() {
        super.viewDidLoad()

        // Listen for pan gesture
        let panGesture = UIPanGestureRecognizer(target: self, action: #selector(onPan(_:)))
        view.addGestureRecognizer(panGesture)
    }

    @objc func onPan(_ panGesture: UIPanGestureRecognizer) {

        func slideViewVerticallyTo(_ y: CGFloat) {
            self.view.frame.origin = CGPoint(x: 0, y: y)
        }

        switch panGesture.state {

        case .began, .changed:
            // If pan started or is ongoing then
            // slide the view to follow the finger
            let translation = panGesture.translation(in: view)
            let y = max(0, translation.y)
            slideViewVerticallyTo(y)

        case .ended:
            // If pan ended, decide it we should close or reset the view
            // based on the final position and the speed of the gesture
            let translation = panGesture.translation(in: view)
            let velocity = panGesture.velocity(in: view)
            let closing = (translation.y > self.view.frame.size.height * minimumScreenRatioToHide) ||
                          (velocity.y > minimumVelocityToHide)

            if closing {
                UIView.animate(withDuration: animationDuration, animations: {
                    // If closing, animate to the bottom of the view
                    self.slideViewVerticallyTo(self.view.frame.size.height)
                }, completion: { (isCompleted) in
                    if isCompleted {
                        // Dismiss the view when it dissapeared
                        dismiss(animated: false, completion: nil)
                    }
                })
            } else {
                // If not closing, reset the view to the top
                UIView.animate(withDuration: animationDuration, animations: {
                    slideViewVerticallyTo(0)
                })
            }

        default:
            // If gesture state is undefined, reset the view to the top
            UIView.animate(withDuration: animationDuration, animations: {
                slideViewVerticallyTo(0)
            })

        }
    }

    override init(nibName nibNameOrNil: String?, bundle nibBundleOrNil: Bundle?)   {
        super.init(nibName: nil, bundle: nil)
        modalPresentationStyle = .overFullScreen;
        modalTransitionStyle = .coverVertical;
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
        modalPresentationStyle = .overFullScreen;
        modalTransitionStyle = .coverVertical;
    }
}



回答7:


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!)
    }
}



回答8:


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.




回答9:


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!
            })
        }
    }



回答10:


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.




回答11:


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];
}



回答12:


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.




回答13:


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)
    }
}



回答14:


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.



来源：https://stackoverflow.com/questions/29290313/in-ios-how-to-drag-down-to-dismiss-a-modal

标签
ios
viewcontroller
gesture-recognition
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