Q118435: INFO: Sharing Menus Between MDI Child Windows

Article: Q118435
Product(s): Microsoft C Compiler
Version(s): 2.1,2.2
Operating System(s): 
Keyword(s): kbnokeyword kbMFC KbUIDesign kbVC100 kbVC150 kbVC152 kbVC200 kbVC210 kbVC220 kbVC400 kb
Last Modified: 07-MAY-2001

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The information in this article applies to:

- Microsoft Visual C++, versions 2.1, 2.2, used with:
   - Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5, 1.52 
   - Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 2.2, 4.0 
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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

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Keywords          : kbnokeyword kbMFC KbUIDesign kbVC100 kbVC150 kbVC152 kbVC200 kbVC210 kbVC220 kbVC400 kbGrpDSMFCATL 
Technology        : kbVCsearch kbAudDeveloper kbVC32bitSearch
Version           : :2.1,2.2
Issue type        : kbinfo

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