抬起手指时如何停止 UIScrollView (Swift 4)

Question

How do I stop a scrollView when the user lifts their fingers instead of just bouncing back to the top?

var displayData = UITextView()

func displayTallTable() {

    displayData.text = outputString
    
    // getFrameBounds (x, y, width, height)
    displayData.frame = CGRect(x: x, y: y, width: w, height: h)
    
    self.addSubview(scrollView)
    scrollView.addSubview(displayData)

    let g = self.safeAreaLayoutGuide
    
    scrollView.leadingAnchor.constraint(equalTo: g.leadingAnchor).isActive = true
    scrollView.trailingAnchor.constraint(equalTo: g.trailingAnchor).isActive = true
    scrollView.topAnchor.constraint(equalTo: g.topAnchor).isActive = true
    scrollView.bottomAnchor.constraint(equalTo: g.bottomAnchor).isActive = true        
}

I can drag the view up but when I lift my fingers, it just bounces back to the top.

So, I added UIScrollViewDelegate to the class:
class TallView: UIView, UIScrollViewDelegate { ... }

and have tried the following, none of which is called:

func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView) {
    debugPrint("scrollViewWillBeginDecelerating")
}
func scrollViewDidScroll(_ scrollView: UIScrollView) {
    debugPrint("scrollViewDidScroll")
}
func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
    debugPrint("scrollViewWillBeginDragging")
}
func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    debugPrint("scrollViewWillEndDragging")
}
func scrollViewDidChangeAdjustedContentInset(_ scrollView: UIScrollView) {
    debugPrint("scrollViewDidChangeAdjustedContentInset")
}

It seems that :

func killScroll() {
    self.scrollView.isScrollEnabled = false;
    self.scrollView.isScrollEnabled = true;
}

(from: How can I programmatically force-stop scrolling in a UIScrollView? ) should do the trick, but I don't know what should be calling it.

What am I missing?

Answer 1

If I understand you correctly, you may want this this effect:

func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if !scrollView.isTracking {
            let contentOffset = scrollView.contentOffset
            // if you want to locate to the top, you could set: let contentOffset = CGPoint.zero
            scrollView.setContentOffset(contentOffset, animated: false)
        }
    }
}