Detect Scroll Up & Scroll down in ListView

Question

I have the following requirement:

• At first, data for page no: 2 is fetched from the server & the items are populated in a ListView.

Considering that both the prev page & next page are available in a scenario, the following code has been added:

 if(prevPageNo > 0){
    mListViewActual.setOnScrollListener(this);
 }

 if(nextPageNo > 0){
    mListViewActual.setOnScrollListener(this);
 }

What conditions should I put to detect scroll up & scroll down on the following methods:

1. void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount)
2. void onScrollStateChanged(AbsListView view, int scrollState)

After the action: scroll up & scroll down is detected , accordingly a service will be called with either the prev page no or next page no , to fetch the items to be populated in the Listview.

Any inputs will be helpful.

Gone through the following links but its not returning the correct scroll up / scroll down action:

link 1 link 2

Answer 1

To also detect scrolling with larger elements, I prefere an onTouch Listener:

listview.setOnTouchListener(new View.OnTouchListener() {

        int scrollEventListSize = 5; 
        float lastY;
        // Used to correct for occasions when user scrolls down(/up) but the onTouchListener detects it incorrectly. We will store detected up-/down-scrolls with -1/1 in this list and evaluate later which occured more often
        List<Integer> downScrolledEventsHappened;

        @Override
        public boolean onTouch(View v, MotionEvent event) {

            float diff = 0;
            if(event.getAction() == event.ACTION_DOWN){
                lastY = event.getY();
                downScrolledEventsHappened = new LinkedList<Integer>();
            }
            else if(event.getAction() == event.ACTION_MOVE){
                diff = event.getY() - lastY;
                lastY = event.getY();

                if(diff>0)
                    downScrolledEventsHappened.add(1);
                else 
                    downScrolledEventsHappened.add(-1);

               //List needs to be filled with some events, will happen very quickly
                if(downScrolledEventsHappened.size() == scrollEventListSize+1){
                    downScrolledEventsHappened.remove(0);
                    int res=0;
                    for(int i=0; i<downScrolledEventsHappened.size(); i++){
                        res+=downScrolledEventsHappened.get(i);
                    }

                    if (res > 0) 
                        Log.i("INFO", "Scrolled up");
                    else 
                        Log.i("INFO", "Scrolled down");
                }
            }
            return false; // don't interrupt the event-chain
        }
    });

Answer 2

Store the firstVisibleItem and on the next onScroll check if the new firstVisibleItem is smaller or greater than the previous one.

Example pseudocode (not tested):

int lastVisibleItem = 0;
boolean isScrollingDown = false;

void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
    if (firstVisibleItem > lastVisibleItem) {
        isScrollingDown = true;
    }
    else {
        isScrollingDown = false;
    }
    lastVisibleItem = firstVisibleItem;
}

Answer 3

My solution works perfectly giving the exact value for each scroll direction. distanceFromFirstCellToTop contains the exact distance from the first cell to the top of the parent View. I save this value in previousDistanceFromFirstCellToTop and as I scroll I compare it with the new value. If it's lower then I scrolled up, else, I scrolled down.

private int previousDistanceFromFirstCellToTop;

listview.setOnScrollListener(new OnScrollListener() {

    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {

    }

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
        View firstCell = listview.getChildAt(0);
        int distanceFromFirstCellToTop = listview.getFirstVisiblePosition() * firstCell.getHeight() - firstCell.getTop();

        if(distanceFromFirstCellToTop < previousDistanceFromFirstCellToTop)
        {
           //Scroll Up
        }
        else if(distanceFromFirstCellToTop  > previousDistanceFromFirstCellToTop)
        {
           //Scroll Down
        }
        previousDistanceFromFirstCellToTop = distanceFromFirstCellToTop;
    }
});

For Xamarin developers, the solution is the following:

Note: don't forget to run on UI thread

listView.Scroll += (o, e) =>
{
    View firstCell = listView.GetChildAt(0);
    int distanceFromFirstCellToTop = listView.FirstVisiblePosition * firstCell.Height - firstCell.Top;

    if (distanceFromFirstCellToTop < previousDistanceFromFirstCellToTop)
    {
        //Scroll Up
    }
    else if (distanceFromFirstCellToTop > previousDistanceFromFirstCellToTop)
    {
        //Scroll Down
    }
    previousDistanceFromFirstCellToTop = distanceFromFirstCellToTop;
};

Answer 4

I've used this much simpler solution:

setOnScrollListener( new OnScrollListener() 
{

    private int mInitialScroll = 0;

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) 
    {
        int scrolledOffset = computeVerticalScrollOffset();

        boolean scrollUp = scrolledOffset > mInitialScroll;
        mInitialScroll = scrolledOffset;
    }


    @Override
    public void onScrollStateChanged(AbsListView view, int scrollState) {


    }

}

Answer 5

Here's what I would try first:

1) Create an interface (let's call it OnScrollTopOrBottomListener) with these methods:

void onScrollTop();

void onScrollBottom();

2) In your list's adapter, add a member instance, typed as the interface you created and supply a setter and getter.

3) In the getView() implementation of your adapter, check if the position parameter is either 0 or getCount() - 1. Also check that your OnScrollTopOrBottomListener instance is not null.

4) If the position is 0, call onScrollTopOrBottomListener.onScrollTop(). If position is getCount() - 1, call onScrollTopOrBottomListener.onScrollBottom().

5) In your OnScrollTopOrBottomListener implementation, call the appropriate methods to get the desired data.

Hope that helps in some way.

-Brandon

Answer 6

            ListView listView = getListView();
            listView.setOnScrollListener(new OnScrollListener() {

                @Override
                public void onScrollStateChanged(AbsListView view, int scrollState) {

                    view.setOnTouchListener(new OnTouchListener() {
                        private float mInitialX;
                        private float mInitialY;

                        @Override
                        public boolean onTouch(View v, MotionEvent event) {
                            switch (event.getAction()) {
                                case MotionEvent.ACTION_DOWN:
                                    mInitialX = event.getX();
                                    mInitialY = event.getY();
                                    return true;
                                case MotionEvent.ACTION_MOVE:
                                    final float x = event.getX();
                                    final float y = event.getY();
                                    final float yDiff = y - mInitialY;
                                    if (yDiff > 0.0) {
                                        Log.d(tag, "SCROLL DOWN");
                                        scrollDown = true;
                                        break;

                                    } else if (yDiff < 0.0) {
                                        Log.d(tag, "SCROLL up");
                                        scrollDown = true;
                                        break;

                                    }
                                    break;
                            }
                            return false;
                        }
                    });