SOLVED Reacting on Treeview user action

I have a dialog with a Treeview.
In the Treeview I can detect when a object is selected or right clicked.

    def ContextMenuCall(self, root, userdata, obj, lColumn, lCommand):
        if lCommand == ID_SHOWTHUMBNAILS:
            # Update dialog according to obj
            return True
        return False

However, in the main dialog I want to react to this right clicking.
How do I 'notify' the main dialog?
I tried sending a message() or SendParentMessage(), but that did not work.