getScrollY StaggerGridView return 0

[amaydiam]

I'm using Android-ParallaxHeaderViewPager and StaggeredGridView to create layout like pinterest. I getting problem when getScrollY, the result is sometimes return 0 when scroll at central position on the first row gird , Where first row grid with 2 column/items and different height each items.

imaging :

this the code :

    @Override
    public void onScroll(AbsListView view, int firstVisibleItem,
                         int visibleItemCount, int totalItemCount, int pagePosition) {
        if (mViewPager.getCurrentItem() == pagePosition && visibleItemCount > 0) {
            int scrollY = getScrollY(view); // sometimes return 0, when scroll at central position on the first row .
        }
    }

 public int getScrollY(AbsListView view) {
        View c = view.getChildAt(0);
        if (c == null) {
            return 0;
        }

        int firstVisiblePosition = view.getFirstVisiblePosition();
        int top = c.getTop();

        int headerHeight = 0;
        if (firstVisiblePosition >= 1) {
            headerHeight = mHeaderHeight;
        }

        return -top + firstVisiblePosition * c.getHeight() + headerHeight;
    }

so how to fix it ?