Messages Used with Menus

The system reports menu-related activity by sending messages to the window procedure of the window that owns the menu. The system 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, see Keyboard Access to Menus.

Next, before displaying any menus, the system sends the

WM_INITMENU

message to the window procedure so that an application can modify the menus before the user sees them. The system sends the

WM_INITMENU

message only once per menu activation.

When the user points to a menu item that opens a submenu, the system 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, the system 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, the system 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.

You can save information for a menu using the

MENUINFO

structure. If the menu is defined with a

MENUINFO.dwStyle

value of MNS_NOTIFYBYPOS, the system sends

WM_MENUCOMMAND

instead of the

WM_COMMAND

when an item is selected. This allows you to access the information in the

MENUINFO

structure and also provides the index of the selected item directly.

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.

The

WM_MENURBUTTONUP

message is sent when the user releases the right mouse button while the cursor is on a menu item. This message is provided so that applications can display a context-sensitive or shortcut menu for a menu item.

There are a few messages that only involve drag-and-drop menus. The

WM_MENUGETOBJECT

is sent to the owner of a drag-and-drop menu when the mouse cursor enters a menu item or moves from the center of an item to the top or the bottom of an item. The

WM_MENUDRAG

message is sent when the user actually drags a menu item.

When a drop-down menu or a submenu has been destroyed, the system sends a

WM_UNINITMENUPOPUP

message.