Swift : Pull down to dismiss `UITableViewController`

Question

I want to pull down to dismiss UITableViewController so I used scrollViewDidScroll method but it didn't works!

    class CommentViewController: PFQueryTableViewController {

        private let tableHeaderHeight: CGFloat = 350.0



extension CommentViewController
{
    override func scrollViewDidScroll(scrollView: UIScrollView)
    {



            // Pull down to dismiss TVC 
            let offsetY = scrollView.contentOffset.y
            let adjustment: CGFloat = 130.0

            // for later use
            if (-offsetY) > (tableHeaderHeight+adjustment) {
                self.dismissViewControllerAnimated(true, completion: nil)
                }
 }
    }

Solution 1

You have to implement additional pan gesture recognizer which will recognize simultaneously with scrollView's pan gesture recognizer. Then you can determine whether user is panning by his finger when table view is already scrolled to the top. e.g.

var isTrackingPanLocation = false
var panGestureRecognizer: UIPanGestureRecognizer!

public override func viewDidLoad() {
    super.viewDidLoad()
    tableView.bounces = false
    panGestureRecognizer = UIPanGestureRecognizer(target: self, 
                                                  action: #selector(panRecognized(gestureRecognizer:)))
    panGestureRecognizer.delegate = self
    tableView.addGestureRecognizer(panGestureRecognizer)
}

public func panRecognized(recognizer: UIPanGestureRecognizer) {
    if recognizer.state == .began && tableView.contentOffset.y == 0 {
        recognizer.setTranslation(CGPoint.zero, inView : tableView)

        isTrackingPanLocation = true
    } else if recognizer.state != .ended && 
              recognizer.state != .cancelled && 
              recognizer.state != .failed && 
              isTrackingPanLocation {
        let panOffset = recognizer.translationInView(tableView)

        // determine offset of the pan from the start here. 
        // When offset is far enough from table view top edge - 
        // dismiss your view controller. Additionally you can 
        // determine if pan goes in the wrong direction and 
        // then reset flag isTrackingPanLocation to false

        let eligiblePanOffset = panOffset.y > 200
        if eligiblePanOffset {
            recognizer.enabled = false
            recognizer.enabled = true
            dismissViewControllerAnimated(true, completion: nil)
        }

        if panOffset.y < 0 {
            isTrackingPanLocation = false
        }
    } else {
        isTrackingPanLocation = false
    }
}

public func gestureRecognizer(gestureRecognizer: UIGestureRecognizer, 
    shouldRecognizeSimultaneouslyWithGestureRecognizer 
                    otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    return true
}

Solution 2

Swift 4

var panGestureRecognizer : UIPanGestureRecognizer!

override func viewDidLoad() {
    mainTableView.bounces = true
    panGestureRecognizer = UIPanGestureRecognizer(target: self, action: #selector(self.panRecognized))
    panGestureRecognizer.delegate = self
    mainTableView.addGestureRecognizer(panGestureRecognizer)
}


@objc func panRecognized(recognizer: UIPanGestureRecognizer) {
    if recognizer.state == .began && mainTableView.contentOffset.y == 0 {

    } else if recognizer.state != .ended && recognizer.state != .cancelled && recognizer.state != .failed {
        let panOffset = recognizer.translation(in: mainTableView)
        let eligiblePanOffset = panOffset.y > 300
        if eligiblePanOffset {
            recognizer.isEnabled = false
            recognizer.isEnabled = true
            self.dismiss(animated: true, completion: nil)
        }
    }
}


func gestureRecognizer(_ gestureRecognizer: UIGestureRecognizer, shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer) -> Bool {
    return true
}

Solution 3

Why don't you place print(offsetY) in scrollViewDidScroll. I suspect that (-offsetY) > (tableHeaderHeight+adjustment) will never be satisfied because of the rubber banding will cause the tableview to rebound before it can dismiss the view controller

Solution 4

For people looking at this in 2019 -- A more modern approach would use the UIGestureRecognizerDelegate methods, instead of keeping extra state in your view controller. For example:

private weak var panFromTop: UIPanGestureRecognizer?

override func viewDidLoad() {
    super.viewDidLoad()

    // Add pan gesture recognizer
    let panFromTop = UIPanGestureRecognizer(target: self, action: #selector(handlePanFromTop(_:)))
    panFromTop.delegate = self
    tableView.addGestureRecognizer(panFromTop)
    self.panFromTop = panFromTop
}

@objc func handlePanFromTop(_ recognizer: UIPanGestureRecognizer) {
    switch recognizer.state {
    case .began:
        // TODO: BEGIN YOUR ANIMATION HERE
    case .changed:
        // TODO: UPDATE YOUR ANIMATION HERE
    default:
        let translation = recognizer.translation(in: view)
        let velocity = recognizer.velocity(in: view)
        if ((translation.y + velocity.y) / view.bounds.height) > 0.5 {
            // TODO: FINISH YOUR ANIMATION HERE
        } else {
            // TODO: CANCEL YOUR ANIMATION HERE
        }
    }
}

Disable bounce at the top of the table view only:

override func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if scrollView.contentOffset.y < 0 {
        scrollView.setContentOffset(.zero, animated: false)
    }
}

Then implement the gesture recognizer delegate methods:

func gestureRecognizer(
    _ gestureRecognizer: UIGestureRecognizer,
    shouldRecognizeSimultaneouslyWith otherGestureRecognizer: UIGestureRecognizer
) -> Bool {
    return true
}

func gestureRecognizerShouldBegin(_ gestureRecognizer: UIGestureRecognizer) -> Bool {
    guard let recognizer = gestureRecognizer as? UIPanGestureRecognizer,
        recognizer === panFromTop else {
        // Only require special conditions for the panFromTop gesture recognizer
        return true
    }

    // Require the scroll view to be at the top,
    // and require the pan to start by dragging downward
    return (
        tableView.contentOffset.y <= 0 &&
        recognizer.velocity(in: view).y > 0
    )
}

View more solutions

Comments

[marrioa]

So I should delete it ? what do you suggest ?

[beyowulf]

place print(-offsetY) in the scrollViewDidScroll before the if statement. build and run your app, pull down on your tableview, look at the values in the console. Do they ever become greater than 480.0?

[marrioa]

What is eligiblePanOffset ?

[Eugene Dudnyk]

That is a flag which is true when user pulled enough to the top. You have to compute it basing on panOffset and 0 - point of table view bounds. E.g. let eligiblePanOffset = (panOffset.y <= -300)

[marrioa]

346.666666666667 this is the result

[marrioa]

I don't know how can you an example

[beyowulf]

So you need to rethink (-offsetY) > (tableHeaderHeight+adjustment) try (-offsetY)> 340.0

[marrioa]

Crashed After scrolling panRecognized:]: unrecognized selector sent to instance 0x7fa29b02a770

[Eugene Dudnyk]

maybe because it's private. Set to public. Let's move to chat conversation.

[Eugene Dudnyk]

Let us continue this discussion in chat.

[Tim Fuqua]

Pretty much interchangeable with UIScrollView as well. This solution is much simpler than others I've seen.

[Thein]

yea, can use with UIScrollView at the same time :) Thanks

[Muhammad Shauket]

After doing this tableview doesn’t scroll anymore

[Eugene Dudnyk]

Check if the method gestureRecognizer (shouldRecognizeSimultaneouslyWithGestureRecognizer: otherGestureRecognizer:) is being called for you. I put it there to ensure that the effect that you described doesn't happen.

[Muhammad Shauket]

it disable tableview scrolling

[latenitecoder]

Cleanest solution on here. Worked out of the box.

[DawnSong]

If you want to scroll up, you need to drag down a little then drag up.

[goodliving]

Great answer, thank you for it! To improve it, don't implement scrollViewDidScroll but add scrollView.isScrollEnabled = false to case .began and true to default in handlePanFromTop.

[Leon Jakonda]

best solution, thx