How to get UIScrollView vertical direction in Swift?

Question

How can I get the scroll/swipe direction for up/down in a VC?

I want to add a UIScrollView or something else in my VC that can see if the user swipes/scrolls up or d

Answer 1

Simply add this method to your view controller:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    if (scrollView.contentOffset.y < 0) {
        // Move UP - Show Navigation Bar
        self.navigationController?.setNavigationBarHidden(false, animated: true)
    } else if (scrollView.contentOffset.y > 0) {
        // Move DOWN - Hide Navigation Bar
        self.navigationController?.setNavigationBarHidden(true, animated: true)
    }
}

Answer 2

I have tried every single response in this thread but none of them could provide a proper solution for a tableView with bounce enabled. So I just used parts of solutions along with some all-time classic boolean flag solution.

1) So, first of all you could use an enum for the scrollDirection:

enum ScrollDirection {
    case up, down
}

2) Set 3 new private vars to help us store lastOffset, scrollDirection and a flag to enable/disable the scroll direction calculation (helps us ignore the bounce effect of tableView) which you will use later:

private var shouldCalculateScrollDirection = false
private var lastContentOffset: CGFloat = 0
private var scrollDirection: ScrollDirection = .up

3) In the scrollViewDidScroll add the following:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    // The current offset
    let offset = scrollView.contentOffset.y

    // Determine the scolling direction
    if lastContentOffset > offset && shouldCalculateScrollDirection {
        scrollDirection = .down
    }
    else if lastContentOffset < offset && shouldCalculateScrollDirection {
        scrollDirection = .up
    }

    // This needs to be in the last line
    lastContentOffset = offset
}

4) If you have not implemented scrollViewDidEndDragging implement it and add these lines of code inside it:

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    guard !decelerate else { return }
    shouldCalculateScrollDirection = false
}

5) If you have not implemented scrollViewWillBeginDecelerating implement it and add this line of code inside it:

func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView) {
    shouldCalculateScrollDirection = false
}

6) Finally, If you have not implemented scrollViewWillBeginDragging implement it and add this line of code inside it:

func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {    
    shouldCalculateScrollDirection = true
}

And if you followed all the steps above you are good to go!

You could go to wherever you want to use the direction and simply write:

switch scrollDirection {
case .up:
    // Do something for scollDirection up
case .down:
    // Do something for scollDirection down
}

Answer 3

you could do something like this:

fileprivate var lastContentOffset: CGPoint = .zero

func checkScrollDirection(_ scrollView: UIScrollView) -> UIScrollViewDirection {
    return lastContentOffset.y > scrollView.contentOffset.y ? .up : .down
}

and with scrollViewDelegate:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    switch checkScrollDirection(scrollView) {
    case .up:
        // move up
    case .down:
        // move down
    default:
        break
    }

    lastContentOffset = scrollView.contentOffset
}

Answer 4

For Swift I think the simplest and most powerful is to do like below. It allows you to track when direction changed and react only once when it changed. Plus you can always access the .lastDirection scrolled property if you need to consult that in your code at any other stage.

enum WMScrollDirection {
    case Up, Down, None
}

class WMScrollView: UIScrollView {
    var lastDirection: WMScrollDirection = .None {
        didSet {
            if oldValue != lastDirection {
                // direction has changed, call your func here
            }
        }
    }

    override var contentOffset: CGPoint {
        willSet {
            if contentOffset.y > newValue.y {
                lastDirection = .Down
            }
            else {
                lastDirection = .Up
            }
        }
    }
}

The above assumes you are only tracking up/down scrolling. It is customizable via the enum. You could add/change to .left and .right to track any direction.

I hope this helps someone.

Cheers

Answer 5

Swift 2-4 with UISwipeGestureRecognizer

Another option, is use to use the UISwipeGestureRecognizer that will recognize the swipe to requested direction (That will work on all views and not only on UIScrollView

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        let upGs = UISwipeGestureRecognizer(target: self, action: #selector(ViewController.handleSwipes(sender:)))
        let downGs = UISwipeGestureRecognizer(target: self, action: #selector(ViewController.handleSwipes(sender:)))
        
        upGs.direction = .up
        downGs.direction = .down
        
        self.view.addGestureRecognizer(upGs)
        self.view.addGestureRecognizer(downGs)
    }

    @objc func handleSwipes(sender:UISwipeGestureRecognizer) {
        
        if (sender.direction == .up) {
            print("Up")
        }
        
        if (sender.direction == .down) {
            print("Down")
        }
    }
}

Answer 6

For swift4

Implement the scrollViewDidScroll method that detects when you pan gesture beyond a y-axis of 0:

public func scrollViewDidScroll(_ scrollView: UIScrollView) {

        if(scrollView.panGestureRecognizer.translation(in: scrollView.superview).y > 0) {
            print("up")
        }
        else {
            print("down")
        }
    }