Advanced MFC Programming

Chapter 2. Menu
}
In the sample, bitmaps are prepared for both checked and unchecked states for a menu item. When
calling function CMenu::SetMenuItemBitmaps(…), if either of the bitmaps is not provided (the
corresponding parameter is NULL), nothing will be displayed for that state. If both parameters are NULL,
the default tick mark will be used for the checked state.
2.5 System Menu and Bitmap Menu Item
System Menu
By default, every application has a system menu, which is accessible through left clicking on the small
icon located at the left side of application’s caption bar, or right clicking on the application when it is in
icon state. The system menu can be customized to meet special requirement. Especially, we can add and
delete menu items dynamically just like a normal menu.
We already know how to access an application’s standard menu. Once we obtained a CMenu type
pointer to the application’s standard menu, we can feel free to add new menu items, remove menu items,
and change their attributes dynamically.
System menu is different from a standard menu. We need to call another function to obtain a pointer to
it. In MFC, the function that can be used to access system menu is CWnd::GetSystemMenu(…). Please note
that we must call this function for a window that has an attached system menu. For an SDI or MDI
application, system menu is attached to the mainframe window. For a dialog box based application, the
system menu is attached to the dialog window.
Unlike user implemented commands, system commands (commands on the system menu) are sent
through WM_SYSCOMMAND rather than WM_COMMAND message. If we implement message handlers to receive
system commands, we need to use ON_WM_SYSCOMMAND macro.
Bitmap Menu Item
From the samples in the previous sections, we already know how to customize a menu item: we can set
check, remove check, change text dynamically. We can also use bitmaps to represent its checked and
unchecked states. Besides above features, a menu item can be modified to display a bitmap instead of a text
string. This can make the application more attractive, because sometimes images are more intuitive than
text strings.
Sample 2.5\Menu demonstrates the two techniques described above, it is based on sample 2.4\Menu.
In this sample, one of the system menu items (a separator) is changed to bitmap menu item. If we execute
this “bitmap command”, a message box will pop up. Also, another new command is added to the system
menu, it allows the user to resume the original system menu.
New Functions
Function CWnd::GetSystemMenu(…) has only one Boolean type parameter:
CMenu *CWnd::GetSystemMenu(BOOL bRevert);
Although we can call this function to obtain a pointer to the system menu and manipulate it, the
original default system menu can be reverted at any time by calling this function and passing a TRUE value
to its bRevert parameter. In this case, function’s returned value has no meaning and should not be treated
as a pointer to a menu object. We need to pass FALSE to this parameter in order to obtain a valid pointer to
the system menu.
Function CMenu::ModifyMenu(…) allows us to change any menu item to a separator, a sub-menu, a
bitmap menu item. It can also be used to modify a menu item’s text. This member function has two
versions:
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