Have any handler or procedure, that call automatic when the click or unclick menu item or button? Similiar SelChangedHandler.
Click and unclick button is call a toggle button. If a menu it can be checked / unchecked. From the help:
"When the user clicks on a ToggleButton, the button toggles between being checked (pushed in) and being unchecked (not pushed in). MapInfo calls the button's handler each time the user clicks on the button. MapInfo's Show Statistics Window button is a ToggleButton. "
For a menu see the function MenuitemInfoByHandler( handler , attribute )
"MENUITEM_INFO_CHECKED Logical: TRUE if the menu item is checkable and currently checked; also return TRUE if the menu item has alternate menu text (e.g. if the menu item toggles between Show... and Hide...), and the menu item is in its "show" state. Otherwise, return FALSE. "