How to override an interface in an MFC application by using Visual C++| Article ID | : | 141277 | | Last Review | : | November 21, 2006 | | Revision | : | 3.1 |
This article was previously published under Q141277 Note Microsoft Visual C++ NET (2002) supported both the managed code
model that is provided by the .NET Framework and the unmanaged native Windows
code model. The information in this article applies to unmanaged Visual C++
code only.
Note Microsoft Visual C++ 2005 supported both the managed code
model that is provided by the .NET Framework and the unmanaged native Windows
code model. SUMMARY In an MFC application, you can override existing interfaces
in a class as well as provide additional interfaces. Overriding an interface in
this case is synonymous with replacing an interface. The example in this
article illustrates how to override an interface in a class while preserving
the original interface implementation so that it can be delegated to by the new
interface implementation. This article does not deal with overriding
the IDispatch implementation, as this is a special case.
For more information about how to override IDispatch in MFC, click the following article number to view the article in the Microsoft Knowledge Base:
140616 (http://support.microsoft.com/kb/140616/)
Replacing MFC IDispatch implementation
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MORE INFORMATION The following steps will override the IOleObject
implementation for a default OLE Control generated by the Control Wizard.
| 1. | To add the declaration of the IOleObject implementation to
the control, add the following code to the header file for the
COleControl-derived class:
// Interface Maps
protected:
// IOleObject
BEGIN_INTERFACE_PART(MyOleObject, IOleObject)
INIT_INTERFACE_PART(CIOleOverCtrl, MyOleObject)
STDMETHOD(SetClientSite)(LPOLECLIENTSITE);
STDMETHOD(GetClientSite)(LPOLECLIENTSITE*);
STDMETHOD(SetHostNames)(LPCOLESTR, LPCOLESTR);
STDMETHOD(Close)(DWORD);
STDMETHOD(SetMoniker)(DWORD, LPMONIKER);
STDMETHOD(GetMoniker)(DWORD, DWORD, LPMONIKER*);
STDMETHOD(InitFromData)(LPDATAOBJECT, BOOL, DWORD);
STDMETHOD(GetClipboardData)(DWORD, LPDATAOBJECT*);
STDMETHOD(DoVerb)(LONG, LPMSG, LPOLECLIENTSITE, LONG, HWND,
LPCRECT);
STDMETHOD(EnumVerbs)(IEnumOLEVERB**);
STDMETHOD(Update)();
STDMETHOD(IsUpToDate)();
STDMETHOD(GetUserClassID)(CLSID*);
STDMETHOD(GetUserType)(DWORD, LPOLESTR*);
STDMETHOD(SetExtent)(DWORD, LPSIZEL);
STDMETHOD(GetExtent)(DWORD, LPSIZEL);
STDMETHOD(Advise)(LPADVISESINK, LPDWORD);
STDMETHOD(Unadvise)(DWORD);
STDMETHOD(EnumAdvise)(LPENUMSTATDATA*);
STDMETHOD(GetMiscStatus)(DWORD, LPDWORD);
STDMETHOD(SetColorScheme)(LPLOGPALETTE);
END_INTERFACE_PART(MyOleObject)
DECLARE_INTERFACE_MAP();
| | 2. | Add the IOleObject interface to the interface map for the
control by adding an INTERFACE_PART macro to the implementation file for the
control:
BEGIN_INTERFACE_MAP(CIOleOverCtrl, COleControl)
INTERFACE_PART(CIOleOverCtrl, IID_IOleObject, MyOleObject)
END_INTERFACE_MAP()
| | 3. | Implement the interface methods you declared. Add the
following code to the implementation file for the control:
STDMETHODIMP_(ULONG) CIOleOverCtrl::XMyOleObject::AddRef()
{
METHOD_MANAGE_STATE(CIOleOverCtrl, MyOleObject)
ASSERT_VALID(pThis);
return pThis->m_xOleObject.AddRef();
}
STDMETHODIMP_(ULONG) CIOleOverCtrl::XMyOleObject::Release()
{
METHOD_MANAGE_STATE(CIOleOverCtrl, MyOleObject)
ASSERT_VALID(pThis);
return pThis->m_xOleObject.Release ();
}
STDMETHODIMP CIOleOverCtrl::XMyOleObject::QueryInterface(
REFIID iid, LPVOID far* ppvObj)
{
METHOD_MANAGE_STATE(CIOleOverCtrl, MyOleObject)
ASSERT_VALID(pThis);
return pThis->m_xOleObject.QueryInterface ( iid, ppvObj);
}
STDMETHODIMP
CIOleOverCtrl::XMyOleObject::SetClientSite(LPOLECLIENTSITE
pClientSite)
{
METHOD_MANAGE_STATE(CIOleOverCtrl, MyOleObject)
ASSERT_VALID(pThis);
return pThis->m_xOleObject.SetClientSite ( pClientSite );
}
... |
The rest of the methods follow the same pattern where
CIOleOverCtrl is the name of the control, XMyOleObject is the name of the
nested class that supports IOleObject, and m_xMyOleObject is calculated by
removing the I from the interface being supported and adding m_x.
Note that these methods simply pass the call on to the original IOleObject
implementation. However, this is not a requirement; you could add functionality
and delegate to the original implementation or not delegate at all.
Back to the top REFERENCES Technical Notes #38 and #39. Back to the top
APPLIES TO| • | Microsoft Foundation Class Library 4.2, when used with: | | | | Microsoft Visual C++ 2.0 Professional Edition | | | | Microsoft Visual C++ 2.1 | | | | Microsoft Visual C++ 2.2 | | | | Microsoft Visual C++ 4.0 Standard Edition | | | | 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++, 32-bit Learning Edition 6.0 | | | | Microsoft Visual C++ .NET 2002 Standard Edition | | | | Microsoft Visual C++ .NET 2003 Standard Edition | | | | Microsoft Visual C++ 2005 Express Edition |
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