Momento design patern with composite patern : I have a rectangle class that extend a form class,  I have a composite class that extend form class, I have a momento class to do a roll back on x and y atrribut of the form.
I have a canvas and I am drawing some shapes on it. by moving one shape it's ok I can undo that move by installing the momento.
The problem is when I group shapes in a composit object of forms, and I move them,  I can't find the way to roll back the move action by installing a momento. Does anyone know how to do that? 