Finding the direction of scrolling in a UIScrollView

Question

I have a UIScrollView with only horizontal scrolling allowed  and I would like to know which direction  left  right  the user scrolls  What I did was to subclass the UIScrollView and override the touchesMoved method   -  void touchesMoved  NSSet   touches withEvent  UIEvent   event        super touchesMoved touches withEvent event        UITouch  touch    touches anyObject       float now    touch locationInView self  x      float before    touch previousLocationInView self  x      NSLog    f  f   before  now       if  now  gt  before           right   NO          NSLog   LEFT              else          right   YES          NSLog   RIGHT                But this method sometimes doesn t get called at all when I move  What do you think

User · Answer

No need to add an extra variable to keep track of this. Just use the UIScrollView's panGestureRecognizer property like this. Unfortunately, this works only if the velocity isn't 0:

CGFloat yVelocity = [scrollView.panGestureRecognizer velocityInView:scrollView].y;
if (yVelocity < 0) {
    NSLog(@"Up");
} else if (yVelocity > 0) {
    NSLog(@"Down");
} else {
    NSLog(@"Can't determine direction as velocity is 0");
}

You can use a combination of x and y components to detect up, down, left and right.

User · Answer

Vertical detection       var lastVelocityYSign   0             func scrollViewDidScroll   scrollView  UIScrollView                    let currentVelocityY    scrollView panGestureRecognizer velocity in  scrollView superview  y                 let currentVelocityYSign   Int currentVelocityY  signum                   if currentVelocityYSign    lastVelocityYSign  amp  amp                      currentVelocityYSign    0                       lastVelocityYSign   currentVelocityYSign                                   if lastVelocityYSign  lt  0                       print  SCROLLING DOWN                     else if lastVelocityYSign  gt  0                       print  SCOLLING UP                                     Answer from Mos6y     https   medium com  Mos6yCanSwift swift-ios-determine-scroll-direction-d48a2327a004

User · Answer

When paging is turned on you could use these code   -  void scrollViewDidEndDecelerating  UIScrollView   scrollView       self lastPage   self currentPage      CGFloat pageWidth    mainScrollView frame size width      self currentPage   floor   mainScrollView contentOffset x - pageWidth   2    pageWidth    1      if  self lastPage  lt  self currentPage              go right         NSLog   right         else if self lastPage  gt  self currentPage             go left         NSLog   left         else if  self lastPage    self currentPage             same page         NSLog   same page

User · Answer

If you work with UIScrollView and UIPageControl  this method will also change the PageControl s page view     func scrollViewWillEndDragging scrollView  UIScrollView  withVelocity velocity  CGPoint  targetContentOffset  UnsafeMutablePointer lt CGPoint gt          let targetOffset   targetContentOffset memory x     let widthPerPage   scrollView contentSize width   CGFloat pageControl numberOfPages       let currentPage   targetOffset   widthPerPage     pageControl currentPage   Int currentPage      Thanks  Esq  s Swift code

User · Answer

Swift 4  For the horizontal scrolling you can simply do   if scrollView panGestureRecognizer translation in  scrollView superview  x  gt  0      print  quot left quot     else      print  quot right quot      For vertical scrolling change  x with  y

User · Answer

Short  amp  Easy would be  just check the velocity value  if its greater than zero then its scrolling left else right   func scrollViewWillEndDragging scrollView  UIScrollView  withVelocity velocity  CGPoint  targetContentOffset  UnsafeMutablePointer lt CGPoint gt          var targetOffset   Float targetContentOffset memory x      println  TargetOffset    targetOffset        println velocity       if velocity x  lt  0           scrollDirection   -1   scrolling left       else           scrollDirection   1   scrolling right

User · Answer

Using scrollViewDidScroll  is a good way to find the current direction    If you want to know the direction after the user has finished scrolling  use the following    property  nonatomic  CGFloat lastContentOffset   -  void scrollViewWillBeginDragging  UIScrollView   scrollView        self lastContentOffset   scrollView contentOffset x     -  void scrollViewDidEndDecelerating  UIScrollView   scrollView        if  self lastContentOffset  lt  scrollView contentOffset x               moved right       else if  self lastContentOffset  gt  scrollView contentOffset x               moved left       else              didn t move

User · Answer

Swift 5 More clean solution with enum for vertical scrolling  enum ScrollDirection       case up  down    var scrollDirection  ScrollDirection        if scrollView panGestureRecognizer translation in  scrollView superview  y  gt  0           return  up       else if scrollView panGestureRecognizer translation in  scrollView superview  y  lt  0           return  down       else           return nil          Usage switch scrollDirection   case  up    print  quot up quot   case  down  print  quot down quot   default     print  quot no scroll quot

User · Answer

I checked some of the answer and elaborated on AnswerBot answer by wrapping everything in a drop in UIScrollView category  The  lastContentOffset  is saved inside the uiscrollview instead and then its just a matter of calling    -  void scrollViewWillBeginDragging  UIScrollView   scrollView      scrollView setLastContentOffset scrollView contentOffset      -  void scrollViewDidEndDragging  UIScrollView   scrollView willDecelerate  BOOL decelerate     if  scrollView scrollDirectionX    ScrollDirectionRight          Do something with your views etc       if  scrollView scrollDirectionY    ScrollDirectionUp          Do something with your views etc         Source code at https   github com tehjord UIScrollViewScrollingDirection

User · Answer

I prefer to do some filtering  based on  memmons s answer  In Objective-C      in the private class extension  property  nonatomic  assign  CGFloat lastContentOffset      in the class implementation -  void scrollViewDidScroll  UIScrollView   scrollView        if  fabs self lastContentOffset - scrollView contentOffset x   gt  20             self lastContentOffset   scrollView contentOffset x             if  self lastContentOffset  gt  scrollView contentOffset x                Scroll Direction Left             do what you need to with scrollDirection here        else               omitted              if  self lastContentOffset  lt  scrollView contentOffset x               do what you need to with scrollDirection here              Scroll Direction Right            When tested in -  void scrollViewDidScroll  UIScrollView   scrollView   NSLog   lastContentOffset  ---  f    scrollView contentOffset x   ---  f   self lastContentOffset  scrollView contentOffset x       self lastContentOffset changes very fast  the value gap is nearly 0 5f   It is not necessary   And occasionally  when handled in accurate condition  your orientation maybe get lost   implementation statements skipped sometimes   such as    -  void scrollViewDidScroll  UIScrollView   scrollView       CGFloat viewWidth   scrollView frame size width       self lastContentOffset   scrollView contentOffset x         Bad example   needs value filtering      NSInteger page   scrollView contentOffset x   viewWidth       if  page    self images count   1  amp  amp  self lastContentOffset  lt  scrollView contentOffset x                  Scroll Direction Right               do what you need to with scrollDirection here                  In Swift 4   var lastContentOffset  CGFloat   0  func scrollViewDidScroll   scrollView  UIScrollView          if  abs lastContentOffset - scrollView contentOffset x   gt  20              lastContentOffset   scrollView contentOffset x               if  lastContentOffset  gt  scrollView contentOffset x                  Scroll Direction Left               do what you need to with scrollDirection here         else                omitted              if  self lastContentOffset  lt  scrollView contentOffset x                do what you need to with scrollDirection here               Scroll Direction Right

User · Answer

In all upper answers two major ways to solve the problem is using panGestureRecognizer or contentOffset  Both methods have their cons and pros   Method 1  panGestureRecognizer  When you use panGestureRecognizer like what  followben suggested  if you don t want to programmatically scroll your scroll view  it works properly    -  void scrollViewWillBeginDragging  UIScrollView   scrollView        if   scrollView panGestureRecognizer translationInView scrollView superview  x  gt  0               handle dragging to the right       else              handle dragging to the left            Cons  But if you move scroll view with following code  upper code can not recognize it   setContentOffset CGPoint x  100  y  0   animation  false    Method 2  contentOffset  var lastContentOffset  CGPoint   CGPoint zero  func scrollViewDidScroll   scrollView  UIScrollView        if  self lastContentOffset x  gt  scrollView contentOffset x               scroll to right       else if self lastContentOffset x  lt  scrollView contentOffset x              scroll to left           self lastContentOffset   self scrollView contentOffset     Cons  If you want to change contentOffset programmatically  during scroll  like when you want to create infinite scroll   this method makes problem  because you might change contentOffset during changing content views places and in this time  upper code jump in that you scroll to right or left

User · Answer

Alternatively  it is possible to observe key path  contentOffset   This is useful when it s not possible for you to set change the delegate of the scroll view    yourScrollView addObserver self forKeyPath   contentOffset  options NSKeyValueObservingOptionNew   NSKeyValueObservingOptionOld context nil     After adding the observer  you could now   -  void observeValueForKeyPath  NSString   keyPath ofObject  id object change  NSDictionary   change context  void   context      CGFloat newOffset     change objectForKey   new   CGPointValue  y      CGFloat oldOffset     change objectForKey   old   CGPointValue  y      CGFloat diff   newOffset - oldOffset      if  diff  lt  0       scrolling down            do something           Do remember to remove the observer when needed  e g  you could add the observer in viewWillAppear and remove it in viewWillDisappear

User · Answer

I would like to know which direction  left  right  the user scrolls    In that case  on iOS 5 and above  use the UIScrollViewDelegate to determine the direction of the user s pan gesture   -  void scrollViewWillBeginDragging  UIScrollView   scrollView        if   scrollView panGestureRecognizer translationInView scrollView superview  x  gt  0               handle dragging to the right       else              handle dragging to the left

User · Answer

In swift       func scrollViewWillBeginDragging   scrollView  UIScrollView        if scrollView panGestureRecognizer translation in  scrollView  y  lt  0           print  down         else           print  up             You can do it also in scrollViewDidScroll

User · Answer

Determining the direction is fairly straightforward  but keep in mind that the direction can change several times over the course of a gesture  For example  if you have a scroll view with paging turned on and the user swipes to go to the next page  the initial direction could be rightward  but if you have bounce turned on  it will briefly be going in no direction at all and then briefly be going leftward   To determine the direction  you ll need to use the UIScrollView scrollViewDidScroll delegate  In this sample  I created a variable named lastContentOffset which I use to compare the current content offset with the previous one  If it s greater  then the scrollView is scrolling right  If it s less then the scrollView is scrolling left      somewhere in the private class extension  property  nonatomic  assign  CGFloat lastContentOffset      somewhere in the class implementation -  void scrollViewDidScroll  UIScrollView   scrollView        ScrollDirection scrollDirection       if  self lastContentOffset  gt  scrollView contentOffset x            scrollDirection   ScrollDirectionRight        else if  self lastContentOffset  lt  scrollView contentOffset x            scrollDirection   ScrollDirectionLeft             self lastContentOffset   scrollView contentOffset x          do whatever you need to with scrollDirection here          I m using the following enum to define direction  Setting the first value to ScrollDirectionNone has the added benefit of making that direction the default when initializing variables   typedef NS ENUM NSInteger  ScrollDirection        ScrollDirectionNone      ScrollDirectionRight      ScrollDirectionLeft      ScrollDirectionUp      ScrollDirectionDown      ScrollDirectionCrazy

User · Answer

Codes explains itself I guess  CGFloat difference1 and difference2 declared in same class private interface  Good if contentSize stays same    -  void scrollViewDidScroll  UIScrollView   scrollView                    CGFloat contentOffSet   scrollView contentOffset y          CGFloat contentHeight   scrollView contentSize height           difference1   contentHeight - contentOffSet           if  difference1  gt  difference2                NSLog   Up             else              NSLog   Down                       difference2   contentHeight - contentOffSet

User · Answer

This is what it worked for me  in Objective-C        -  void scrollViewDidScroll  UIScrollView   scrollView           NSString  direction     scrollView panGestureRecognizer translationInView scrollView superview  y  gt 0    up    down           NSLog       direction

User · Answer

Ok so for me this implementation is working really good    property  nonatomic  assign  CGPoint lastContentOffset    -  void scrollViewWillBeginDragging  UIScrollView   scrollView        lastContentOffset x   scrollView contentOffset x       lastContentOffset y   scrollView contentOffset y       -  void scrollViewDidEndDecelerating  UIScrollView   scrollView        if   lastContentOffset x  lt   int scrollView contentOffset x               moved right         NSLog   right              else if   lastContentOffset x  gt   int scrollView contentOffset x               moved left         NSLog   left          else if   lastContentOffset y lt  int scrollView contentOffset y           NSLog   up          else if   lastContentOffset y gt  int scrollView contentOffset y           NSLog   down             self txtText resignFirstResponder              So this will fire textView to dismiss after drag ends

User · Answer

Swift 2 2 Simple solution which tracks single and multiple directions  without any loss        Keep last location with parameter   var lastLocation CGPoint   CGPointZero       We are using only this function so  we can      track each scroll without lose anyone   override func scrollViewWillBeginDragging scrollView  UIScrollView        let currentLocation   scrollView contentOffset         Add each direction string     var directionList  String            if lastLocation x  lt  currentLocation x           print  right         directionList append  Right         else if lastLocation x  gt  currentLocation x           print  left         directionList append  Left                 there is no  else if  to track both vertical        and horizontal direction     if lastLocation y  lt  currentLocation y           print  up         directionList append  Up         else if lastLocation y  gt  currentLocation y           print  down         directionList append  Down                 scrolled to single direction     if directionList count    1         print  scrolled to   directionList 0   direction          else if directionList count  gt  0       scrolled to multiple direction       print  scrolled to   directionList 0  -  directionList 1   direction                  Update last location after check current otherwise         values will be same     lastLocation   scrollView contentOffset

User · Answer

-  void scrollViewWillEndDragging  UIScrollView   scrollView withVelocity  CGPoint velocity targetContentOffset  inout CGPoint   targetContentOffset   NSLog   px  f py  f  velocity x velocity y      Use this delegate method of scrollview   If y co-ordinate of velocity is  ve scroll view scrolls downwards and if it is -ve scrollview scrolls upwards  Similarly left and right scroll can be detected using x co-ordinate

User · Answer

Here is my solution for behavior like in  followben answer  but without loss with slow start  when dy is 0    property  assign  nonatomic  BOOL isFinding   property  assign  nonatomic  CGFloat previousOffset   -  void scrollViewWillBeginDragging  UIScrollView   scrollView       self isFinding   YES    -  void scrollViewDidScroll  UIScrollView   scrollView       if  self isFinding            if  self previousOffset    0                self previousOffset   self tableView contentOffset y             else               CGFloat diff   self tableView contentOffset y - self previousOffset              if  diff    0                    self previousOffset   0                  self isFinding   NO                   if  diff  gt  0                           moved up                   else                          moved down

User · Answer

In iOS8 Swift I used this method     override func scrollViewDidScroll scrollView  UIScrollView        var frame  CGRect   self photoButton frame     var currentLocation   scrollView contentOffset y      if frame origin y  gt  currentLocation          println  Going up         else if frame origin y  lt  currentLocation          println  Going down               frame origin y   scrollView contentOffset y   scrollHeight     photoButton frame   frame     view bringSubviewToFront photoButton       I have a dynamic view which changes locations as the user scrolls so the view can seem like it stayed in the same place on the screen  I am also tracking when user is going up or down   Here is also an alternative way   func scrollViewWillEndDragging scrollView  UIScrollView  withVelocity velocity  CGPoint  targetContentOffset  UnsafeMutablePointer lt CGPoint gt         if targetContentOffset memory y  lt  scrollView contentOffset y           println  Going up          else           println  Going down

User · Answer

-  void scrollViewWillEndDragging  UIScrollView   scrollView withVelocity  CGPoint velocity targetContentOffset  inout CGPoint   targetContentOffset        CGPoint targetPoint    targetContentOffset      CGPoint currentPoint   scrollView contentOffset       if  targetPoint y  gt  currentPoint y            NSLog   up              else           NSLog   down

User · Answer

The solution  func scrollViewDidScroll scrollView  UIScrollView         if scrollView panGestureRecognizer translationInView scrollView superview  y  gt  0                  print  up              else                print  down

[iphone] Finding the direction of scrolling in a UIScrollView?

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