How to get the scroll speed on a ListView?

Question

I have a ListView with onScrollStateChanged and onScroll event listeners. I want to be able to get the scroll speed of the ListView or some way to get the finalX location of

Answer 1

Division first visible items difference on time difference is not a good solution. OnScroll listener recieves onScroll event every fixed period of time, so in most cases the result of division will be "0".

So you can try something like this:

private OnScrollListener onScrollListener = new OnScrollListener() {

    private int previousFirstVisibleItem = 0;
    private long previousEventTime = 0;
    private double speed = 0;

    @Override
    public void onScroll(HtcAbsListView view, int firstVisibleItem,
            int visibleItemCount, int totalItemCount) {

        if (previousFirstVisibleItem != firstVisibleItem){
            long currTime = System.currentTimeMillis();
            long timeToScrollOneElement = currTime - previousEventTime;
            speed = ((double)1/timeToScrollOneElement)*1000;

            previousFirstVisibleItem = firstVisibleItem;
            previousEventTime = currTime;

            Log.d("DBG", "Speed: " +speed + " elements/second");
        }

    }

    @Override
    public void onScrollStateChanged(HtcAbsListView view, int scrollState) {
    }
};