Detect parent absoulte position change

I'm making a control that is like a combo box. The popup listbox is a child of the desktop window and I need to keep it synchronized with the absolute (screen) position of the parent dialog (which change when you are dragging the window).

How to do this from the control ? An easy way would have to track dialog position change in the dialog but I don't want to have to do anything in the dialog.

Subclass the parent window and intercept the WM_WINDOWPOSCHANGED (or WM_MOVE/WM_SIZE)

-Safai