To identify the type of control that was dropped, use the source argument of the DragDrop event.
This script for the DragDrop event in a picture declares two variables, then determines the type of object that was dropped:
CommandButton lcb_button
StaticText lst_info
IF source.TypeOf() = CommandButton! THEN
lcb_button = source
lcb_button.Text = "You dropped a Button!"
ELSEIF source.TypeOf() = StaticText! THEN
lst_info = source
lst_info.Text = "You dropped the text!"
END IF