method private _cb__view_to_selection_changed = fun () ->
    match select_w#view2.SW.st_view#selection#get_selected_rows with
      | [path] ->
          let iter = select_w#store2#get_iter path in
          let (_, cmodel) = select_w#store2#get_data ~row:iter in
            self#_set_constr_model cmodel;
            glade#add_constr_button#misc#set_sensitive true
      | _ ->
          self#_set_constr_model empty_constr_store;
          glade#add_constr_button#misc#set_sensitive false