private void updateRecyclerViewScrollState(RecyclerView recyclerView) {
        if (recyclerView.getChildCount() == 0) {
            setDraggable(true);
        } else {
            RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
            int[] i = new int[1];
            if (layoutManager instanceof LinearLayoutManager || layoutManager instanceof GridLayoutManager) {
                i[0] = ((LinearLayoutManager) layoutManager).findFirstVisibleItemPosition();
            } else if (layoutManager instanceof StaggeredGridLayoutManager) {
                i = null;
                i = ((StaggeredGridLayoutManager) layoutManager).findFirstVisibleItemPositions(i);
            }
            if (i[0] == 0) {
                View firstChild = recyclerView.getChildAt(0);
                if (firstChild.getTop() == recyclerView.getPaddingTop()) {
                    setDraggable(true);
                    return;
                }
            }
            setDraggable(false);
        }
    }
Set associated list view, then this layout will only be able to drag down when the list
view is scrolled to top.

@param recyclerView
scrolllayout/src/main/java/com/yinglan/scrolllayout/ScrollLayout.java