BMenu¶
A BMenu object displays a pull-down or pop-up list of menu items. A menu can contain
simple menu items (BMenuItem objects), or other menus (other BMenus). To
add an item to a menu, call AddItem().
Menu Hierarchy¶
Menus are hierarchically arranged; an item in one menu can control another menu. The controlled menu is a submenu; the menu that contains the item that controls it is its supermenu. A submenu remains hidden until the user operates the item that controls it; it becomes hidden again when the user is finished with it.
The menu at the root of the hierarchy is displayed in a window as a list - perhaps a list of just
one item. Since it, unlike other menus, doesn’t have a controlling item, it must remain visible. A
root menu is therefore a special kind of menu in that it behaves more like an ordinary view than do
other menus, which stay hidden. Root menus should belong to the BMenuBar class, which
is derived from BMenu. The typical root menu is a menu bar displayed across the top of
a window.
Menu Items¶
Each item in a menu is a kind of BMenuItem object. An item can be marked (displayed
with a check mark to its left), assigned a keyboard shortcut, enabled and disabled, and given a
“trigger” character that the user can type to invoke the item when its menu is open on-screen.
Every item has a particular job to do. If an item controls a submenu, its job is to show the submenu
on-screen and hide it again. All other items give instructions to the application. When invoked by
the user, they deliver a BMessage to a target BHandler. What the item does
depends on the content of the BMessage and the BHandlers response to it.