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Messages Used with Menus
Windows reports menu-related activity by sending messages to the window
procedure of the window that owns the menu. Windows sends a series of messages when
the user selects items on the menu bar or clicks the right mouse button to
display a shortcut menu.
When the user activates an item on the menu bar, the owner window first
receives a WM_SYSCOMMAND message. This message includes a flag that indicates whether the user
activated the menu by using the keyboard (SC_KEYMENU) or the mouse (SC_MOUSEMENU). For
more information about the keyboard interface for menus, see Keyboard Access to Menus.
Next, before displaying any menus, Windows sends the WM_INITMENU message to the window procedure so that an application can modify the menus
before the user sees them. Windows sends the WM_INITMENU message only once per
menu activation.
When the user points to a menu item that opens a submenu, Windows sends the
owner window the WM_INITMENUPOPUP message before displaying the submenu. This message gives the application an
opportunity to modify the submenu before it is displayed.
Each time the user moves the highlighting from one item to another, Windows
sends a WM_MENUSELECT message to the window procedure of the menu's owner window. This message
identifies the currently selected menu item. Many applications provide an
information area at the bottom of their main windows and use this message to display
additional information about the selected menu item.
When the user chooses a command item from a menu, Windows sends a WM_COMMAND message to the window procedure. The low-order word of the WM_COMMAND
message's wParam parameter contains the identifier of the chosen item. The window procedure
should examine the identifier and process the message accordingly.
Not all menus are accessible through a window's menu bar. Many applications
display shortcut menus when the user clicks the right mouse button at a specific
location. Such applications should process the WM_CONTEXTMENU message and display a shortcut menu, if appropriate. If an application does
not display a shortcut menu, it should pass the WM_CONTEXTMENU message to the DefWindowProc function for default processing.
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