HOWTO: SubClass the MDIClient by Using MFC

ID: Q129471

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, 1.51, 1.52
- Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 2.1, 4.0, 4.1, 4.2, 5.0, 6.0

SUMMARY

In MFC, the MDICLIENT window is stored in a public HWND member variable (m_hwndMDIClient) within the CMDIFrameWnd class. CMDIFrameWnd is the base class of the CMainFrame class in an AppWizard-generated MDI application.

There are three steps required to subclass the MDICLIENT window:

Use ClassWizard to derive a class from CWnd called CMDIClientWnd.

Add the function, GetSuperWndProcAddr(), to CMDIClientWnd.

Use CMDIClientWnd to subclass the MDICLIENT window.

Once the MDICLIENT window has been subclassed with CMDIClientWnd, message handlers and other functions can be placed in the CMDIClientWnd class.

MORE INFORMATION

Here is more detailed information about each of the steps:

Use ClassWizard to derive a class from CWnd called CMDIClientWnd.

For details on how to derive a class using ClassWizard, please see the User's Guide documentation on ClassWizard, specifically the "Adding a New Class" section.

Add the function GetSuperWndProcAddr() to CMDIClientWnd.

NOTE: This step need only be performed if you are using 16-bit versions of Visual C++, not 32-bit. The 32-bit versions of Visual C++ implement this functionality for you.

Once the class has been created, add the following prototype to the header file:
```
      public:
          WNDPROC* GetSuperWndProcAddr(); 
```
And add the following function to the .CPP file:
```
      WNDPROC* CMDIClientWnd::GetSuperWndProcAddr() {
          static WNDPROC NEAR pfnSuper = NULL;
          return &pfnSuper;
      } 
```

Use CMDIClientWnd to subclass the MDICLIENT window in the CMDIFrameWnd class (usually CMainFrame).

To the CMainFrame class, add a public variable of type CMDIClientWnd called m_wndMDIClient. Then modify OnCreate for CMainFrame as follows:


      int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)
      {
          if (CMDIFrameWnd::OnCreate(lpCreateStruct) == -1)
          return -1;

          if (!m_wndMDIClient.SubclassWindow (m_hWndMDIClient)) { // Add
              TRACE ("Failed to subclass MDI client window\n");   // Add
              return (-1);                                        // Add
          }                                                       // Add
      ...
      }

After completing these three steps, you can use ClassWizard to add message handlers to CMDIClientWnd similar to the one below, which changes the MDICLIENT's background color.


BOOL CMDIClientWnd::OnEraseBkgnd(CDC* pDC)
{
  // Set brush to desired background color
  CBrush backBrush(RGB(255, 128, 128));

  // Save old brush
  CBrush* pOldBrush = pDC->SelectObject(&backBrush);

  CRect rect;
  pDC->GetClipBox(&rect);     // Erase the area needed
  pDC->PatBlt(rect.left, rect.top, rect.Width(), rect.Height(),
      PATCOPY);
  pDC->SelectObject(pOldBrush);
  return TRUE;
}

Additional query words:

Keywords : kbprg kbtool kbnokeyword kbMFC kbVC kbVC100 kbVC150 kbVC152 kbVC200 kbVC410 kbVC420 kbVC500 kbVC600
Version : 1.0 1.5 1.52 2.0 4.1 4.2 5.0 6.0
Platform : NT WINDOWS
Issue type : kbhowto