android - smoothScrollToPositionFromTop() is not always working like it should

Question

I've been trying for a while to get smoothScrollToPositionFromTop() working, but it doesn't always scroll to the correct position.

I've got a ListView (with 10 items) in a layout with 10 buttons on the side, so I can scroll to every item in the list. Usually when I scroll one position back or forward it works fine, but often when I try to scroll more then 3 positions back or forward the ListView does not exactly end at the selected position. When it fails, it usually ends up 0,5 to 1,5 items off and it is not really predictable when the scroll fails.

I have also checked out smoothScrollToPosition after notifyDataSetChanged not working in android, but this fix is not working for me and I don't change any data.

I would really like to automatically scroll to the selected listitems, but not I can't figure out how. Has anybody had this problem before and knows how to fix it?

Answer 1

This is a known bug. See https://code.google.com/p/android/issues/detail?id=36062

However, I implemented this workaround that deals with all edge cases that might occur:

First call smothScrollToPositionFromTop(position) and then, when scrolling has finished, call setSelection(position). The latter call corrects the incomplete scrolling by jumping directly to the desired position. Doing so the user still has the impression that it is being animation-scrolled to this position.

I implemented this workaround within two helper methods:

smoothScrollToPositionFromTop()

public static void smoothScrollToPositionFromTop(final AbsListView view, final int position) {
    View child = getChildAtPosition(view, position);
    // There's no need to scroll if child is already at top or view is already scrolled to its end
    if ((child != null) && ((child.getTop() == 0) || ((child.getTop() > 0) && !view.canScrollVertically(1)))) {
        return;
    }

    view.setOnScrollListener(new AbsListView.OnScrollListener() {
        @Override
        public void onScrollStateChanged(final AbsListView view, final int scrollState) {
            if (scrollState == SCROLL_STATE_IDLE) {
                view.setOnScrollListener(null);

                // Fix for scrolling bug
                new Handler().post(new Runnable() {
                    @Override
                    public void run() {
                        view.setSelection(position);
                    }
                });
            }
        }

        @Override
        public void onScroll(final AbsListView view, final int firstVisibleItem, final int visibleItemCount,
                                 final int totalItemCount) { }
    });

    // Perform scrolling to position
    new Handler().post(new Runnable() {
        @Override
        public void run() {
            view.smoothScrollToPositionFromTop(position, 0);
        }
    });
}

getChildAtPosition()

public static View getChildAtPosition(final AdapterView view, final int position) {
    final int index = position - view.getFirstVisiblePosition();
    if ((index >= 0) && (index < view.getChildCount()))?{
        return view.getChildAt(index);
    } else {
        return null;
    }
}