How to get UIScrollView vertical direction in Swift?

If you use an UIScrollView then you can take benefit from the scrollViewDidScroll: function. You need to save the last position (the contentOffset) it have and the update it like in the following way:

// variable to save the last position visited, default to zero

 private var lastContentOffset: CGFloat = 0

 func scrollViewDidScroll(_ scrollView: UIScrollView) {
     if (self.lastContentOffset > scrollView.contentOffset.y) {
         // move up
     }
     else if (self.lastContentOffset < scrollView.contentOffset.y) {
        // move down
     }

     // update the new position acquired
     self.lastContentOffset = scrollView.contentOffset.y
     print(lastContentOffset)
 }

There are other ways of doing it of course this is one of them.

I hope this helps you.

Victor's answer is great, but it's quite expensive, as you're always comparing and storing values. If your goal is to identify the scrolling direction instantly without expensive calculation, then try this using Swift:

func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
    let translation = scrollView.panGestureRecognizer.translation(in: scrollView.superview)
    if translation.y > 0 {
        // swipes from top to bottom of screen -> down
    } else {
        // swipes from bottom to top of screen -> up
    }
}

And there you go. Again, if you need to track constantly, use Victors answer, otherwise I prefer this solution. 😊

I used Victor's answer with a minor improvement. When scrolling past the end or beginning of the scroll, and then getting the bounce back effect. I have added the constraint by calculating scrollView.contentSize.height - scrollView.frame.height and then limiting the scrollView.contentOffset.y range to be greater than 0 or less than scrollView.contentSize.height - scrollView.frame.height, no changes are made when bouncing back.

func scrollViewDidScroll(_ scrollView: UIScrollView) {

    if lastContentOffset > scrollView.contentOffset.y && lastContentOffset < scrollView.contentSize.height - scrollView.frame.height {
        // move up
    } else if lastContentOffset < scrollView.contentOffset.y && scrollView.contentOffset.y > 0 {
        // move down
    }

    // update the new position acquired
    lastContentOffset = scrollView.contentOffset.y
}