Can I have onScrollListener for a ScrollView

Question

I am using a HorizontalScrollView in a layout and I need to identify the user have reached the start and end point of the scroll   For ListView I have tried a the onScrollListener and it is possible to find the start and end point of scroll   I tried to do the same in my Scrollview but it seems not possible  Is there any other possible ways to achieve what I need

User · Answer

--------Start Scroll Bar Slide--------     final HorizontalScrollView xHorizontalScrollViewHeader    HorizontalScrollView  findViewById R id HorizontalScrollViewHeader       final HorizontalScrollView xHorizontalScrollViewData    HorizontalScrollView  findViewById R id HorizontalScrollViewData       xHorizontalScrollViewData getViewTreeObserver   addOnScrollChangedListener new ViewTreeObserver OnScrollChangedListener              Override         public void onScrollChanged                 int scrollX  int scrollY              scrollX xHorizontalScrollViewData getScrollX                scrollY xHorizontalScrollViewData getScrollY                xHorizontalScrollViewHeader scrollTo scrollX  scrollY                            ---------End Scroll Bar Slide---------

User · Answer

If you want to know the scroll position of a view  then you can use the following extension function on View class   fun View  onScroll callback   x  Int  y  Int  - gt  Unit        var oldX   0     var oldY   0     this  viewTreeObserver  addOnScrollChangedListener           if  oldX    scrollX    oldY    scrollY                callback scrollX  scrollY              oldX   scrollX             oldY   scrollY

User · Answer

You can use NestedScrollView instead of ScrollView  However  when using a Kotlin Lambda  it won t know you want NestedScrollView s setOnScrollChangeListener instead of the one at View  which is API level 23   You can fix this by specifying the first parameter as a NestedScrollView   nestedScrollView setOnScrollChangeListener      NestedScrollView  scrollX  Int  scrollY  Int     Int     Int - gt      Log d  ScrollView    Scrolled to  scrollX   scrollY

User · Answer

you can define a custom ScrollView class   amp  add an interface be called when scrolling like this   public class ScrollChangeListenerScrollView extends HorizontalScrollView     private MyScrollListener mMyScrollListener   public ScrollChangeListenerScrollView Context context        super context      public ScrollChangeListenerScrollView Context context  AttributeSet attrs        super context  attrs      public ScrollChangeListenerScrollView Context context  AttributeSet attrs  int defStyleAttr        super context  attrs  defStyleAttr       public void setOnMyScrollListener MyScrollListener myScrollListener       this mMyScrollListener   myScrollListener       Override protected void onScrollChanged int l  int t  int oldl  int oldt        super onScrollChanged l  t  oldl  oldt       if mMyScrollListener  null           mMyScrollListener onScrollChange this l t oldl oldt             public interface MyScrollListener       void onScrollChange View view int scrollX int scrollY int oldScrollX  int oldScrollY

User · Answer

Beside accepted answer  you need to hold a reference of listener and remove when you don t need it  Otherwise you will get a null pointer exception for your ScrollView and memory leak  mentioned in comments of accepted answer    You can implement OnScrollChangedListener in your activity fragment  MyFragment   ViewTreeObserver OnScrollChangedListener   Add it to scrollView when your view is ready  scrollView viewTreeObserver addOnScrollChangedListener this    Remove listener when no longer need  ie  onPause    scrollView viewTreeObserver removeOnScrollChangedListener this

User · Answer

Here s a derived HorizontalScrollView I wrote to handle notifications about scrolling and scroll ending   It properly handles when a user has stopped actively scrolling and when it fully decelerates after a user lets go  public class ObservableHorizontalScrollView extends HorizontalScrollView       public interface OnScrollListener           public void onScrollChanged ObservableHorizontalScrollView scrollView  int x  int y  int oldX  int oldY           public void onEndScroll ObservableHorizontalScrollView scrollView              private boolean mIsScrolling      private boolean mIsTouching      private Runnable mScrollingRunnable      private OnScrollListener mOnScrollListener       public ObservableHorizontalScrollView Context context            this context  null  0              public ObservableHorizontalScrollView Context context  AttributeSet attrs            this context  attrs  0              public ObservableHorizontalScrollView Context context  AttributeSet attrs  int defStyle            super context  attrs  defStyle               Override     public boolean onTouchEvent MotionEvent ev            int action   ev getAction             if  action    MotionEvent ACTION MOVE                mIsTouching   true              mIsScrolling   true            else if  action    MotionEvent ACTION UP    action    MotionEvent ACTION CANCEL                if  mIsTouching  amp  amp   mIsScrolling                    if  mOnScrollListener    null                        mOnScrollListener onEndScroll this                                                mIsTouching   false                     return super onTouchEvent ev               Override     protected void onScrollChanged int x  int y  int oldX  int oldY            super onScrollChanged x  y  oldX  oldY            if  Math abs oldX - x   gt  0                if  mScrollingRunnable    null                    removeCallbacks mScrollingRunnable                              mScrollingRunnable   new Runnable                     public void run                         if  mIsScrolling  amp  amp   mIsTouching                            if  mOnScrollListener    null                                mOnScrollListener onEndScroll ObservableHorizontalScrollView this                                                                        mIsScrolling   false                      mScrollingRunnable   null                                                postDelayed mScrollingRunnable  200                      if  mOnScrollListener    null                mOnScrollListener onScrollChanged this  x  y  oldX  oldY                        public OnScrollListener getOnScrollListener             return mOnScrollListener             public void setOnScrollListener OnScrollListener mOnEndScrollListener            this mOnScrollListener   mOnEndScrollListener

User · Answer

Every instance of View calls getViewTreeObserver    Now when holding an instance of ViewTreeObserver  you can add an OnScrollChangedListener   to it using the method addOnScrollChangedListener     You can see more information about this class here   It lets you be aware of every scrolling event - but without the coordinates  You can get them by using getScrollY   or getScrollX   from within the listener though   scrollView getViewTreeObserver   addOnScrollChangedListener new OnScrollChangedListener          Override     public void onScrollChanged             int scrollY   rootScrollView getScrollY       For ScrollView         int scrollX   rootScrollView getScrollX       For HorizontalScrollView            DO SOMETHING WITH THE SCROLL COORDINATES

User · Answer

This might be very useful  Use NestedScrollView instead of ScrollView  Support Library 23 1 introduced an OnScrollChangeListener to NestedScrollView  So you can do something like this    myScrollView setOnScrollChangeListener new NestedScrollView OnScrollChangeListener              Override         public void onScrollChange NestedScrollView v  int scrollX  int scrollY  int oldScrollX  int oldScrollY                Log d  ScrollView   scrollX   scrollX   scrollY   scrollY   oldScrollX   oldScrollX   oldScrollY   oldScrollY                 Do something

[android] Can I have onScrollListener for a ScrollView?

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