Knowledge Base

How to override the default behavior of several of the MFC control container interface methods in Visual C++

Article ID: 196835

Article Last Modified on 6/1/2005

APPLIES TO

Microsoft Foundation Class Library 4.2, when used with:
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 6.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Professional Edition
- Microsoft Visual C++ 6.0 Professional Edition
- Microsoft Visual C++ 6.0 Standard Edition

This article was previously published under Q196835

SUMMARY

The MFC that ships with Microsoft Visual C++ 5.0 provides some very basic control container support. The majority of this containment support is implemented in undocumented or private classes. As an advanced procedure, it is possible to derive from these classes and override the default behavior of several of the MFC control container interface methods.

WARNING: This functionality is based on private header files and classes of MFC and as such must be considered version specific. These files are subject to change and therefore, you use them at your own risk. If you use this article, Microsoft Technical Support will not be able to assist with any problems as this article uses undocumented classes.

MORE INFORMATION

The MFC control container support involves three main classes: COccManager, COleControlContainer, and COleControlSite. COccManager is the master- controller for all control containers in one MFC process and is responsible for handing out pointers to COleControlSite and COleControlContainer objects. COccManager also has an IsDialogMessage method that implements message processing functionality needed by ActiveX control containers.

COleControlContainer implements the container for one or more ActiveX controls. This container corresponds to one particular window in the container application that hosts several ActiveX controls and other standard controls. Typically, this is a dialog box. As the container object, COleControlContainer implements two interfaces: IOleInPlaceFrame and IOleContainer.

For each control hosted in the control container object, there is a corresponding MFC control site object. This control site object is implemented by COleControlSite. As the one-on-one direct site object for a hosted ActiveX control, the COleControlSite implements several interfaces: IOleClientSite, IOleInPlaceSite, IOleControlSite, IPropertyNotifySink, IBoundObjectSite, INotifyDBEvents. COleControlSite also implements two IDispatch interfaces, one for ambient properties and the other as an event sink for the control.

This article provides the steps required to override one of these three objects to change or add functionality at the interface level in COleControlContainer or COleControlSite.

Steps to override COleControlContainer

Create a class derived from COleControlContainer. The constructor needs to call the COleControlContainer constructor directly, as there is no default COleControlContainer constructor:
```
      CMyOleControlContainer::CMyOleControlContainer(CWnd* pWnd) :
         COleControlContainer(pWnd)
      {
      }
                    
```
Create a class derived from COccManager. Add an empty constructor and an empty virtual destructor.

Override the COccManager::CreateContainer function to create and return a new instance of your new COleControlContainer-derived class. You can do this by adding the following method to your COccManager class definition:

      virtual COleControlContainer* CreateContainer(CWnd* pWnd)
      {
         // Advanced control container applications may want to override.
         return new CMyOleControlContainer(pWnd);
      }

Modify your call to AfxEnableControlContainer (probably in CYourApp::InitInstance) to pass in an instance of your COccManager-derived class:
```
      CMyOccManager theManager;

      // ...

      BOOL CMfcaxscrvbApp::InitInstance()
      {
         // Initialize OLE libraries
         if (!AfxOleInit())
         // ...
         AfxEnableControlContainer(&theManager);
                    
```
NOTE: For a CHtmlView derived class, its Create function calls AfxEnableControlContainer() causing it to override our initial custom COccManager class. To avoid this problem, you need to override CHtmlView::Create, copy all the code into your overridden Create function minus the call to AfxEnableC ntrolContainer(). Remember NOT to call the base class Create method since the original implementation did not.
Include the Occimpl.h header file in your CMyOccManager implementation file before the CMyOccManager header file. You may need to make a direct reference in the #include statement because Occimpl.h is in the VC/MFC/SRC directory.

Include the Occimpl.h header file in your CMyOleControlContainer implementation file before the CMyOleControlContainer header file. Use the AFX_DATA defines to insure that you import data from the classes defined in Occimpl.h:

      #undef AFX_DATA
      #define AFX_DATA AFX_DATA_IMPORT
      #include "c:\program files\devstudio\vc\mfc\src\occimpl.h"
      #undef AFX_DATA
      #define AFX_DATA AFX_DATA_EXPORT

Follow the standard procedure to override an interface in the CMyOleControlContainer class. For more information about how to do this, click the following article number to view the article in the Microsoft Knowledge Base:

141277 How to override an interface in an MFC application

Here is a typical example that overrides the IOleInPlaceFrame interface:

      // Inside header definition in .h.
      class CMyOleControlContainer : public COleControlContainer
      {
      // ...
         // Interface maps.
         BEGIN_INTERFACE_PART(MyOleIPFrame, IOleInPlaceFrame)
            INIT_INTERFACE_PART(CMyOleControlContainer, MyOleIPFrame)
            STDMETHOD(GetWindow)(HWND*);
            STDMETHOD(ContextSensitiveHelp)(BOOL);
            STDMETHOD(GetBorder)(LPRECT);
            STDMETHOD(RequestBorderSpace)(LPCBORDERWIDTHS);
            STDMETHOD(SetBorderSpace)(LPCBORDERWIDTHS);
            STDMETHOD(SetActiveObject)(LPOLEINPLACEACTIVEOBJECT,
                                       LPCOLESTR);
            STDMETHOD(InsertMenus)(HMENU, LPOLEMENUGROUPWIDTHS);
            STDMETHOD(SetMenu)(HMENU, HOLEMENU, HWND);
            STDMETHOD(RemoveMenus)(HMENU);
            STDMETHOD(SetStatusText)(LPCOLESTR);
            STDMETHOD(EnableModeless)(BOOL);
            STDMETHOD(TranslateAccelerator)(LPMSG, WORD);
         END_INTERFACE_PART(MyOleIPFrame)

         DECLARE_INTERFACE_MAP()
      };

      // Inside implementation file .cpp:

      BEGIN_INTERFACE_MAP(CMyOleControlContainer, COleControlContainer)
         INTERFACE_PART(CMyOleControlContainer, IID_IOleInPlaceFrame,
                        MyOleIPFrame)
      END_INTERFACE_MAP()

      STDMETHODIMP CMyOleControlContainer::XMyOleIPFrame::QueryInterface(
         REFIID iid, LPVOID* ppvObj)
      {
         METHOD_PROLOGUE_EX_(CMyOleControlContainer, MyOleIPFrame)
         return (HRESULT)pThis->InternalQueryInterface(&iid, ppvObj);
      }

      STDMETHODIMP_(ULONG) CMyOleControlContainer::XMyOleIPFrame::AddRef()
      {
         METHOD_PROLOGUE_EX_(CMyOleControlContainer, MyOleIPFrame)
         return (ULONG)pThis->InternalAddRef();
      }

      // ...
      // Cut and paste all of this code from the MFC source in Occimpl.h
      // and change all references to COleControlContainer to reference
      // your class. Then, modify methods as desired. For example, here is
      // a customized enablemodeless call:

      STDMETHODIMP
         CMyOleControlContainer::XMyOleIPFrame::EnableModeless(BOOL f)
      {
         METHOD_PROLOGUE_EX(CMyOleControlContainer, MyOleIPFrame)

         CWinApp* pApp = AfxGetApp();
         if (!pApp)
            return E_FAIL;

         pApp->EnableModeless(f);
         return S_OK;
      }

Steps to override COleControlSite

To override COleControlSite, follow the same steps as for COleControlContainer, substituting COleControlSite for COleControlContainer where appropriate. Some relevant code snippets follow:

   CMyOleControlSite::CMyOleControlSite(COleControlContainer* pCtrlCont) :
      COleControlSite(pCtrlCont)
   {

   }

The COccManager::CreateSite is used to create COleControlSite objects. To use your ControlSite class, add the following method to your COccManager class definition:

   virtual COleControlSite* CreateSite(COleControlContainer* pCtrlCont)
   {
      // advanced control container override
      return new CMyOleControlSite(pCtrlCont);
   }

A typical example that overrides the IOleControlSite interface follows:

   // Inside header definition in .h:
   class CMyOleControlSite : public COleControlSite
   {
   // ...
      // Interface maps.
      BEGIN_INTERFACE_PART(MyOleControlSite, IOleControlSite)
         INIT_INTERFACE_PART(CMyOleControlSite, MyOleControlSite)
         STDMETHOD(OnControlInfoChanged)();
         STDMETHOD(LockInPlaceActive)(BOOL fLock);
         STDMETHOD(GetExtendedControl)(LPDISPATCH* ppDisp);
         STDMETHOD(TransformCoords)(POINTL* lpptlHimetric,
            POINTF* lpptfContainer, DWORD flags);
         STDMETHOD(TranslateAccelerator)(LPMSG lpMsg, DWORD grfModifiers);
         STDMETHOD(OnFocus)(BOOL fGotFocus);
         STDMETHOD(ShowPropertyFrame)();
      END_INTERFACE_PART(MyOleControlSite)

      DECLARE_INTERFACE_MAP()
   };

   // Inside implementation file .cpp:

      BEGIN_INTERFACE_MAP(CMyOleControlSite, CMyOleControlSite)
         INTERFACE_PART(CMyOleControlSite, IID_IOleControlSite,
                        MyOleControlSite)
      END_INTERFACE_MAP()

   STDMETHODIMP_(ULONG) CMyOleControlSite::XMyOleControlSite::AddRef()
   {
      METHOD_PROLOGUE_EX_(CMyOleControlSite, OleControlSite)
      return (ULONG)pThis->InternalAddRef();
   }

   STDMETHODIMP_(ULONG) CMyOleControlSite::XMyOleControlSite::Release()
   {
      METHOD_PROLOGUE_EX_(CMyOleControlSite, OleControlSite)
      return (ULONG)pThis->InternalRelease();
   }

   // ...
   // Cut and paste all of this code from the MFC source in Occimpl.h
   // and change all references to COleControlSite to reference your
   // class. Then, modify methods as desired.

REFERENCES

For more information about how to override an interface in an MFC application, click the following article number to view the article in the Microsoft Knowledge Base: