How to detect when a UIScrollView has finished scrolling In Swift

Question

There was, by all accounts, an excellent solution to this problem in Obj-C presented by Ashley Smart (How to detect when a UIScrollView has finished scrolling).

-(void)scrollViewDidScroll:(UIScrollView *)sender 
{   
[NSObject cancelPreviousPerformRequestsWithTarget:self];
    //ensure that the end of scroll is fired.
    [self performSelector:@selector(scrollViewDidEndScrollingAnimation:) withObject:nil afterDelay:0.3]; 

...
}

-(void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView
{
    [NSObject cancelPreviousPerformRequestsWithTarget:self];
...
}

I need a solution, however, in Swift.

It appears that the excellent delay function, contributed by Matt (dispatch_after - GCD in swift?) is likely to help.

func delay(delay:Double, closure:()->()) {
    dispatch_after(
        dispatch_time(
            DISPATCH_TIME_NOW,
            Int64(delay * Double(NSEC_PER_SEC))
        ),
        dispatch_get_main_queue(), closure)
}

and implemented as ...

delay(0.4) {
    // do stuff
}

but I've still not put it together. Any help?

score 31 · Accepted Answer · edited Jan 30 '19 at 14:15

31

The delegate method tells you when finished

func scrollViewDidEndDecelerating(scrollView: UIScrollView) {
    self.stoppedScrolling()
}

func scrollViewDidEndDragging(scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    if !decelerate {
        self.stoppedScrolling()
    }
}

func stoppedScrolling() {
    println("Scroll finished")
}

edited Jan 30 '19 at 14:15

Iulian Onofrei

9,188
10
67
113

answered Jun 01 '15 at 20:28

Nekak Kinich

905
7
10

2

This doesn't work in case the scroll has no deceleration towards the stop point, which may be very well when the user lifts his finger, so you may consider scrollViewDidEndDragging as well. – Bogdan Feb 23 '17 at 08:33
And even scrollViewDidEndScrollingAnimation, I didn't considered it earlier too :) – Bogdan Feb 24 '17 at 11:07

score 11 · Answer 2 · answered Jan 02 '17 at 16:20

The scrollViewDidEndDecelerating won't be called if user is scrolling slowly. Here's Ashley Smart asnwear in Swift

func scrollViewDidScroll(_ scrollView: UIScrollView) {
    NSObject.cancelPreviousPerformRequests(withTarget: self)
    perform(#selector(UIScrollViewDelegate.scrollViewDidEndScrollingAnimation), with: nil, afterDelay: 0.3)
}

func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
    NSObject.cancelPreviousPerformRequests(withTarget: self)
// Call your function here
}

score 5 · Answer 3 · answered Mar 10 '17 at 14:08

There is a method of UIScrollViewDelegate which can be used to detect (or better to say 'predict') when scrolling has really finished:

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>)

of UIScrollViewDelegate which can be used to detect (or better to say 'predict') when scrolling has really finished.

In my case I used it with horizontal scrolling as following (in Swift 3):

func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
    perform(#selector(self.actionOnFinishedScrolling), with: nil, afterDelay: Double(velocity.x))
}
func actionOnFinishedScrolling() {
    print("scrolling is finished")
    // do what you need
}

score 3 · Answer 4 · edited Apr 17 '18 at 11:49

3

You need to check whether the user has stopped dragging and if the view is still decelerating after the user stopped dragging:

func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
    if collectionView.isDecelerating == false {
        // Perform whichever function you desire for when scrolling has stopped
    }
}

func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
    // Perform whichever function you desire for when scrolling has stopped
}

edited Apr 17 '18 at 11:49

Akhrameev

325
4
12

answered Jan 27 '17 at 04:45

Ever Uribe

639
6
13

What is the diference between checking `isDecelerating` vs checking the param `decelerate`? – AmiguelS Nov 29 '17 at 16:02

score 0 · Answer 5 · answered Aug 28 '17 at 18:31

Swift Version:

NOTE: The answer you mentioned is a possible solution and differ with cases

func scrollViewDidScroll(_ scrollView: UIScrollView) {

        // YOUR CODE........
        NSObject.cancelPreviousPerformRequests(withTarget: self)
        self.perform(#selector(scrollViewDidEndScrollingAnimation(_:)), with: scrollView, afterDelay: 0.3)
    }

    func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {


        // YOUR CODE ........
        NSObject.cancelPreviousPerformRequests(withTarget: self)
    }

How to detect when a UIScrollView has finished scrolling In Swift

5 Answers5