public View findTopChildUnder(int x, int y) {
        final int childCount = mParentView.getChildCount();
        for (int i = childCount - 1; i >= 0; i--) {
            final View child = mParentView.getChildAt(mCallback.getOrderedChildIndex(i));
            if (x >= child.getLeft() && x < child.getRight() &&
                    y >= child.getTop() && y < child.getBottom()) {
                return child;
            }
        }
        return null;
    }
Find the topmost child under the given point within the parent view's coordinate system.
The child order is determined using {@link Callback#getOrderedChildIndex(int)}.

@param x X position to test in the parent's coordinate system
@param y Y position to test in the parent's coordinate system
@return The topmost child view under (x, y) or null if none found.
app/src/main/java/home/smart/fly/animations/widget/slidepanel/ViewDragHelper.java