How to detect when a UIScrollView has finished scrolling

Question

UIScrollViewDelegate has got two delegate methods scrollViewDidScroll  and scrollViewDidEndScrollingAnimation  but neither of these tell you when scrolling has completed  scrollViewDidScroll only notifies you that the scroll view did scroll not that it has finished scrolling   The other method scrollViewDidEndScrollingAnimation only seems to fire if you programmatically move the scroll view not if the user scrolls   Does anyone know of scheme to detect when a scroll view has completed scrolling

User · Answer

If somebody needs  here s Ashley Smart answer 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

User · Answer

I think scrollViewDidEndDecelerating is the one you want  Its UIScrollViewDelegates optional method   -  void scrollViewDidEndDecelerating  UIScrollView   scrollView   Tells the delegate that the scroll view has ended decelerating the scrolling movement    UIScrollViewDelegate documentation

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Swift version of accepted answer    func scrollViewDidScroll scrollView  UIScrollView            example code   func scrollViewDidEndDragging scrollView  UIScrollView  willDecelerate decelerate  Bool               example code   func scrollViewDidEndZooming scrollView  UIScrollView  withView view  UIView   atScale scale  CGFloat             example code

User · Answer

On some earlier iOS versions like iOS 9  10   scrollViewDidEndDecelerating won t be triggered if the scrollView is suddenly stopped by touching    But in the current version  iOS 13   scrollViewDidEndDecelerating will be triggered for sure  As far as I know    So  if your App targeted earlier versions as well  you might need a workaround like the one mentioned by Ashley Smart  or you can the following one        func scrollViewDidEndDecelerating   scrollView  UIScrollView            if  scrollView isTracking   scrollView isDragging   scrollView isDecelerating      1             scrollViewDidEndScrolling scrollView                       func scrollViewDidEndDragging   scrollView  UIScrollView  willDecelerate decelerate  Bool            if  decelerate  scrollView isTracking   scrollView isDragging   scrollView isDecelerating      2             scrollViewDidEndScrolling scrollView                       func scrollViewDidEndScrolling   scrollView  UIScrollView               Do something here         Explanation  UIScrollView will be stoped in three ways  - quickly scrolled and stopped by itself - quickly scrolled and stopped by finger touch  like Emergency brake  - slowly scrolled and stopped  The first one can be detected by scrollViewDidEndDecelerating and other similar methods while the other two can t   Luckily  UIScrollView has three statuses we can use to identify them  which is used in the two lines commented by    1  and    2

User · Answer

I ve tried Ashley Smart s answer and it worked like a charm  Here s another idea  with using only scrollViewDidScroll  - void scrollViewDidScroll  UIScrollView   sender           if self scrollView Result contentOffset x    self scrollView Result frame size width                 You have reached page 1           I just had two pages so it worked for me  However  if you have more than one page  it could be problematic  you could check whether the current offset is a multiple of the width but then you wouldn t know if the user stopped at 2nd page or is on his way to 3rd or more

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I only just found this question  which is pretty much the same I asked  How to know exactly when a UIScrollView  39 s scrolling has stopped   Though didEndDecelerating works when scrolling  panning with stationary release does not register   I eventually found a solution  didEndDragging has a parameter WillDecelerate  which is false in the stationary release situation   By checking for  decelerate in DidEndDragging  combined with didEndDecelerating  you get both situations that are the end of scrolling

User · Answer

For all scrolls related to dragging interactions  this will be sufficient   -  void scrollViewDidEndDecelerating  UIScrollView   scrollView        isScrolling   NO     -  void scrollViewDidEndDragging  UIScrollView   scrollView willDecelerate  BOOL decelerate       if   decelerate             isScrolling   NO            Now  if your scroll is due to a programmatic setContentOffset scrollRectVisible  with animated   YES or you obviously know when scroll is ended     -  void scrollViewDidEndScrollingAnimation         isScrolling   NO      If your scroll is due to something else  like keyboard opening or keyboard closing   it seems like you ll have to detect the event with a hack because scrollViewDidEndScrollingAnimation is not useful either   The case of a PAGINATED scroll view   Because  I guess  Apple apply an acceleration curve  scrollViewDidEndDecelerating get called for every drag so there s no need to use scrollViewDidEndDragging in this case

User · Answer

UIScrollview has a delegate method  -  void scrollViewDidEndDecelerating  UIScrollView   scrollView   Add the below lines of code in the delegate method  -  void scrollViewDidEndDecelerating  UIScrollView   scrollView   CGSize scrollview content scrollView contentSize  CGPoint scrollview offset scrollView contentOffset  CGFloat size scrollview content width  CGFloat x scrollview offset x  if   size-self view frame size width   x          You have reached last page

User · Answer

If you re into Rx  you can extend UIScrollView like this   import RxSwift import RxCocoa  extension Reactive where Base  UIScrollView       public var didEndScrolling  ControlEvent lt Void gt            let source   Observable              merge  base rx didEndDragging map     0                        base rx didEndDecelerating mapTo true                 filter    0                mapTo             return ControlEvent events  source            which will allow you to just do like this   scrollView rx didEndScrolling subscribe onNext           Do what needs to be done here      This will take into account both dragging and deceleration

User · Answer

Just developed solution to detect when scrolling finished app-wide  https   gist github com k06a 731654e3168277fb1fd0e64abc7d899e  It is based on idea of tracking changes of runloop modes  And perform blocks at least after 0 2 seconds after scrolling   This is core idea for tracking runloop modes changes iOS10    -  void tick         NSRunLoop mainRunLoop  performInModes    UITrackingRunLoopMode   block             self tock              -  void tock       self runLoopModeWasUITrackingAgain   YES        NSRunLoop mainRunLoop  performInModes    NSDefaultRunLoopMode   block             self tick               And solution for low deployment targets like iOS2    -  void tick         NSRunLoop mainRunLoop  performSelector  selector tock  target self argument nil order 0 modes    UITrackingRunLoopMode        -  void tock       self runLoopModeWasUITrackingAgain   YES        NSRunLoop mainRunLoop  performSelector  selector tick  target self argument nil order 0 modes    NSDefaultRunLoopMode

User · Answer

This has been described in some of the other answers  but here s  in code  how to combine scrollViewDidEndDecelerating and scrollViewDidEndDragging willDecelerate to perform some operation when scrolling has finished   -  void scrollViewDidEndDecelerating  UIScrollView   scrollView        self stoppedScrolling      -  void scrollViewDidEndDragging  UIScrollView   scrollView                    willDecelerate  BOOL decelerate       if   decelerate             self stoppedScrolling            -  void stoppedScrolling          done  do whatever

User · Answer

func scrollViewDidEndDecelerating   scrollView  UIScrollView        scrollingFinished scrollView  scrollView     func scrollViewDidEndDragging   scrollView  UIScrollView  willDecelerate decelerate  Bool        if decelerate             didEndDecelerating will be called for sure         return           scrollingFinished scrollView  scrollView             func scrollingFinished scrollView  UIScrollView          Your code

User · Answer

Using Ashley Smart logic and is being converted into Swift 4 0 and above        func scrollViewDidScroll   scrollView  UIScrollView             NSObject cancelPreviousPerformRequests withTarget  self          perform  selector UIScrollViewDelegate scrollViewDidEndScrollingAnimation       with  scrollView  afterDelay  0 3             func scrollViewDidEndScrollingAnimation   scrollView  UIScrollView            NSObject cancelPreviousPerformRequests withTarget  self          The logic above solve issues such as when user is scrolling off the tableview  Without the logic  when you scroll off the tableview  didEnd will be called but it will not execute anything  Currently using it in year 2020

User · Answer

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 lt CGPoint gt     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 lt CGPoint gt         perform  selector self actionOnFinishedScrolling   with  nil  afterDelay  Double velocity x     func actionOnFinishedScrolling         print  scrolling is finished          do what you need

User · Answer

The 320 implementations are so much better - here is a patch to get consistent start ends of the scroll   - void scrollViewDidScroll  UIScrollView   sender        NSObject cancelPreviousPerformRequestsWithTarget self         ensure that the end of scroll is fired       self performSelector  selector scrollViewDidEndScrollingAnimation   withObject sender afterDelay 0 3            - void scrollViewDidEndScrollingAnimation  UIScrollView   scrollView        NSObject cancelPreviousPerformRequestsWithTarget self

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An alternative would be to use scrollViewWillEndDragging withVelocity targetContentOffset which is called whenever the user lifts the finger and contains the target content offset where the scroll will stop  Using this content offset in scrollViewDidScroll  correctly identifies when the scroll view has stopped scrolling   private var targetY  CGFloat  public func scrollViewWillEndDragging   scrollView  UIScrollView                                        withVelocity velocity  CGPoint                                        targetContentOffset  UnsafeMutablePointer lt CGPoint gt            targetY   targetContentOffset pointee y   public func scrollViewDidScroll   scrollView  UIScrollView        if  scrollView contentOffset y    targetY            print  finished scrolling

User · Answer

-  void scrollViewDidEndDecelerating  UIScrollView   scrollView        self stoppedScrolling      -  void scrollViewDidEndDragging  UIScrollView   scrollView willDecelerate  BOOL decelerate       if   decelerate             self stoppedScrolling            -  void stoppedScrolling

User · Answer

To recap  and for newbies   It s not that painful  Just add the protocol  then add the functions you need for detection   In the view  class  that contains the UIScrolView  add the protocol  then added any the functions from here to your view  class       --------------------------------    In the  h  file     --------------------------------  interface myViewClass   UIViewController   lt UIScrollViewDelegate gt      lt -- Adding the protocol here     Scroll view  property  nonatomic  retain  UIScrollView  myScrollView   property  nonatomic  assign  BOOL isScrolling      Protocol functions -  void scrollViewWillBeginDragging  UIScrollView   scrollView -  void scrollViewDidEndDecelerating  UIScrollView   scrollView  -  void scrollViewDidEndDragging  UIScrollView   scrollView       --------------------------------    In the  m  file     --------------------------------  implementation BlockerViewController  -  void viewDidLoad       CGRect scrollRect   self view frame     Same size as this view     self myScrollView     UIScrollView alloc  initWithFrame scrollRect       self myScrollView delegate   self      self myScrollView contentSize   CGSizeMake scrollRect size width  scrollRect size height       self myScrollView contentInset   UIEdgeInsetsMake 0 0 22 0 0 0 22 0          Allow dragging button to display outside the boundaries     self myScrollView clipsToBounds   NO         Prevent buttons from activating scroller      self myScrollView canCancelContentTouches   NO      self myScrollView delaysContentTouches   NO       self myScrollView setBackgroundColor  UIColor darkGrayColor         self view addSubview self myScrollView           Add stuff to scrollview     UIImage  myImage    UIImage imageNamed   foo png         self myScrollView addSubview myImage         Protocol functions -  void scrollViewWillBeginDragging  UIScrollView   scrollView       NSLog   start drag         isScrolling   YES     -  void scrollViewDidEndDecelerating  UIScrollView   scrollView       NSLog   end decel         isScrolling   NO     -  void scrollViewDidEndDragging  UIScrollView   scrollView willDecelerate  BOOL decelerate       NSLog   end dragging        if   decelerate            isScrolling   NO              All of the available functions are here     https   developer apple com library ios documentation UIKit Reference UIScrollViewDelegate Protocol Reference UIScrollViewDelegate html

User · Answer

I had a case of tapping and dragging actions and I found out that the dragging was calling scrollViewDidEndDecelerating  And the change offset manually with code    scrollView setContentOffset contentOffset animated YES    was calling scrollViewDidEndScrollingAnimation     This delegate method is called when the dragging scrolling happens  but no when the     tapping -  void scrollViewDidEndDecelerating  UIScrollView   scrollView         do whatever you want to happen when the scroll is done      This delegate method is called when the tapping scrolling happens  but no when the  dragging - void scrollViewDidEndScrollingAnimation  UIScrollView   scrollView          do whatever you want to happen when the scroll is done

[ios] How to detect when a UIScrollView has finished scrolling

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