Advanced MFC Programming

Chapter 2. Menu
in class CMenuDoc, whose function names are OnEditInsertDynamicMenu,
OnUpdateEditInsertDynamicMenu, OnEditDeleteDynamicMenu and OnUpdateEditDeleteDynamicMenu.
Because we want to disable command ID_EDIT_DELETEDYNAMICMENU and enable command
ID_EDIT_INSERTDYNAMICMENU before the sub-menu is inserted, and reverse this after the menu is inserted,
another Boolean type variable m_bSubMenuOn is declared in class CMenuDoc, which will be used to indicate
the state of the inserted menu. It is initialized to FALSE in the constructor.
Preparing the menu resource that will be used to implement dynamic sub-menu is the same with what
we did in the previous sample. Here a resource IDR_MENU_POPUP is added to the application, whose content
is the same with the resource created in sample 2.2\Menu.
In this case, we could not use a local variable to load the menu, because once the menu is inserted, it
may exist for a while before the user removes it. If we still use a local variable, it will go out of scope after
the messagae hander returns. In the sample, a CMenu type variable is declared in class CMenuDoc, which is
used to load the menu resource in the constructor.
The following shows the modified class CMenuDoc:
……
class CMenuDoc : public CDocument
{
protected: // create from serialization only
CMenu m_menuSub;
BOOL m_bSubMenuOn;
protected:
//{{AFX_MSG(CMenuDoc)
afx_msg void OnEditInsertDynamicMenu();
afx_msg void OnUpdateEditInsertDynamicMenu(CCmdUI* pCmdUI);
afx_msg void OnEditDeleteDynamicMenu();
afx_msg void OnUpdateEditDeleteDynamicMenu(CCmdUI* pCmdUI);
//}}AFX_MSG
DECLARE_MESSAGE_MAP()
};
The following is the constructor within which the menu resource is loaded and m_bSubMenuOn is
initialized:
CMenuDoc::CMenuDoc()
{
m_menuSub.LoadMenu(IDR_MENU_POPUP);
m_bSubMenuOn=FALSE;
}
The following shows two UPDATE_COMMAND_UI message handlers where two menu commands are
enabled or disabled:
void CMenuDoc::OnUpdateEditInsertDynamicMenu(CCmdUI* pCmdUI)
{
pCmdUI->Enable(m_bSubMenuOn == FALSE);
}
void CMenuDoc::OnUpdateEditDeleteDynamicMenu(CCmdUI* pCmdUI)
{
pCmdUI->Enable(m_bSubMenuOn == TRUE);
}
At last, we must implement two WM_COMMAND message handlers. First, we need to find a way of
accessing mainframe menu IDR_MAINFRAME of the application. In MFC, a menu associated with a window
can be accessed by calling function CWnd::GetMenu(), which will return a CMenu type pointer. Once we get
this pointer, we can use it to access any of its sub-menus.
The mainframe window pointer can be obtained by calling function AfxGetMainWnd() anywhere in the
program. An alternate way is to call AfxGetApp() to obtain a CWinApp type pointer, then access its public
member m_pMainWnd. We could use CMenu type pointer to insert or remove a sub-menu dynamically.
The following shows two message handlers that are used to insert or remove the sub-menu:
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