Sharing Menus Between MDI Child Windows

ID: Q118435

The information in this article applies to:

The Microsoft Foundation Classes (MFC), included with:
- Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0

SUMMARY

The document-template model used in the MFC assumes that each template will have its own set of distinct resources that are all identified by the same resource ID. However, when dealing with similar MDI child windows, you may want to conserve resource space and have MDI child windows share the same menu resource.

MORE INFORMATION

Each CMultiDocTemplate object has a member variable, "m_hMenuShared", that stores the handle of the menu to be used for that child window. However, because the default CMultiDocTemplate object assumes that it is the only user of this member variable, a new class (for example, CSharedDocTemplate) must be derived to avoid having the CMultiDocTemplate destructor call DestroyMenu on the shared menu handle:


   class CSharedDocTemplate : public CMultiDocTemplate
   {
     public:
       CSharedDocTemplate(UINT nIDResource, CRuntimeClass* pDocClass,
           CRuntimeClass* pFrameClass, CRuntimeClass* pViewClass);

       virtual ~CSharedDocTemplate();
   };

   CSharedDocTemplate::CSharedDocTemplate(UINT nIDResource,
     CRuntimeClass* pDocClass, CRuntimeClass* pFrameClass,
     CRuntimeClass* pViewClass) : CMultiDocTemplate(nIDResource, pDocClass,
                                    pFrameClass, pViewClass)
   {
   }

   CSharedDocTemplate::~CSharedDocTemplate()
   {
     // This prevents the base class virtual destructor from
     // destroying the menu resource (i.e. its checks to make
     // sure the handle isn't NULL)

     m_hMenuShared = NULL;
   }

At this point, declare a public member variable to hold the common menu for the application; the CWinApp-derived object will take the responsibility of loading and destroying the common menu.


   class CMyApp : public CWinApp
   {
   public:
      HMENU m_ghMenuShared;

      //...
   };

Now, after the CSharedDocTemplate object has been created, you need to set its public member variable to the common menu resouce for the application. The following code fragments demonstrate how to set the handle for a single template or traverse the template list and set the common handle for all CSharedDocTemplate objects. Either of these code fragments could be used in the InitInstance of the CWinApp-derived object:


   BOOL CMyApp::InitInstance()
   {
      ...

      // New member of CWinApp derived class to store menu handle
      m_ghMenuShared = ::LoadMenu(m_hInstance,
         MAKEINTRESOURCE(IDR_SHAREDMENU));

      CSharedDocTemplate* pDocTemplate;
      pDocTemplate = new CSharedDocTemplate(
                         IDR_MYTYPE,  // No menu resource should exist for
                                      // this ID, the menu is set manually
                         RUNTIME_CLASS(CMDIMyDoc),
                         RUNTIME_CLASS(CMDIChildWnd),
                         RUNTIME_CLASS(CMDIMyView));
      pDocTemplate->m_hMenuShared = m_ghMenuShared;
      AddDocTemplate(pDocTemplate);

      ...
   }

-or-


   BOOL CMyApp::InitInstance()
   {
      ...

      m_ghMenuShared = ::LoadMenu(m_hInstance,
         MAKEINTRESOURCE(IDR_SHAREDMENU));

      if (!m_templateList.IsEmpty())
      {
         CDocTemplate *pDocTemplate;

         for (POSITION rPos = m_templateList.GetHeadPosition();
            rPos != NULL;)
         {
            pDocTemplate = m_templateList.GetNext(rPos);
            if (pDocTemplate->IsKindOf(RUNTIME_CLASS(CSharedDocTemplate)))
               ((CSharedDocTemplate *)pDocTemplate)->m_hMenuShared =
                                                     m_ghMenuShared;
         }
      }

      ...
   }

Lastly, you need to destroy the menu resource loaded in InitInstance. This can easily be accomplished by overriding the ExitInstance member of the CWinApp-derived class:


   int CMyApp::ExitInstance()
   {
      ::DestroyMenu(m_ghMenuShared);
   }

Additional query words: kbinf 1.00 1.50 2.00 2.10 2.50 3.00 4.00


Keywords          : kbnokeyword kbMFC kbVC 
Version           : 1.00 1.50 | 1.00 2.00 4.00
Platform          : NT WINDOWS 
Issue type        :

Last Reviewed: July 30, 1999