sticky header in nested RecyclerView (android)

Question

I try to implement a sticky header as Sevastyan Savanyuk said in:
How can I make sticky headers in RecyclerView? (Without external lib)

I have a nested recycler view in an outer recycler view. I just want my inner recycler view has a sticky header. But onDrawOver method just called once.
The result is that I draw the header in my onDrawOver, but it's not sticky!

I only have one sticky header(item 0), here's my code(kotlin):

    override fun isHeader(itemPosition: Int): Boolean = itemPosition == 0

    override fun getHeaderPositionForItem(itemPosition: Int): Int = 0

here's my onDrawOver method:

@Override
public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
    super.onDrawOver(c, parent, state);
    View topChild = parent.getChildAt(0);
    if (topChild == null) {
        return;
    }

    int topChildPosition = parent.getChildAdapterPosition(topChild);
    if (topChildPosition == RecyclerView.NO_POSITION) {
        return;
    }

    int headerPos = mListener.getHeaderPositionForItem(topChildPosition);
    View currentHeader = getHeaderViewForItem(headerPos, parent);
    fixLayoutSize(parent, currentHeader);
    int contactPoint = currentHeader.getBottom();
    View childInContact = getChildInContact(parent, contactPoint, headerPos);

    if (childInContact != null) {
        int itemPosition = parent.getChildAdapterPosition(childInContact);
        if (mListener.isHeader(itemPosition)) {
            moveHeader(c, currentHeader, childInContact);
            return;
        }
    }

    drawHeader(c, currentHeader);
}

How can I get my header sticky, why does onDrawOver method just called once, help!