How to get UIScrollView vertical direction in Swift?

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 down and then hide/show a UIView depending if it was an up/down gesture.

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
}

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

I hope this help 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
}

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")
    }
 }