Creating our own menu and adding
items to such menus is a common phenomenon. But adding a menu
item to a menu already created by framework like system menu is
rather uncommon. Here is the article which demonstrates how to
add a new menu item to the system menu. The way an application
calls CWnd::GetMenu( ) to obtain a CMenu
pointer to its top-level menu, likewise, it can call CWnd::GetSystemMenu( ) to obtain a pointer to its
system menu. This is what has been done in the OnCreate( )
handler. The FALSE parameter passed to the
GetSystemMenu( ) indicates that you want a pointer to a
copy of the system menu that you can modify. Passing TRUE resets
the system menu to its default state. Once the pointer to the
system menu is obtained, the AppendMenu( ) function is
called once to add a separator and then to add the 'About' menu
item. Note that the ID for this menu item has been given as 112.
This is because it is necessary that the IDs of system menu
items are multiples of 16 and the 'About' menu item happens to
be the seventh menu item. When the user clicks on an item from
the system menu, the window receives a WM_SYSCOMMAND message. We
have tackled this message using the handler OnSysCommand( ).
The first parameter passed to it contains the ID of the
menu item selected in the upper 12 bits. The lower 4 bits are
used by Windows internally. Hence, the id has been Ended with
0xFFF0 to strip off any bits that Windows may have added to it.
If the 'About' menu item is selected then an appropriate message
is displayed using the MessageBox( ) function. It is
necessary to call the base class's OnSysCommand( )
handler so that the selection of other system menu items gets
properly processed. Download |