CODEWITHSUNDEEP
iosswiftuiscrollview
Don Hall
Don Hall

Reputation: 145

How to detect when a UIScrollView has finished scrolling In Swift

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?

Upvotes: 14

Views: 27552

Answers (5)

Nekak Kinich
Nekak Kinich

Reputation: 934

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")
}

Upvotes: 32

Ever Uribe
Ever Uribe

Reputation: 669

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
}

Upvotes: 4

Abhishek Thapliyal
Abhishek Thapliyal

Reputation: 3718

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)
    }

Upvotes: 0

lexpenz
lexpenz

Reputation: 61

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
}

Upvotes: 5

Xernox
Xernox

Reputation: 1736

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
}

Upvotes: 11

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