How to Use MFC to Step Through Child Windows of the MDIClient

WINDOWS             | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52
      - Microsoft Visual C++, 32-bit Edition, versions 1.0, 2.0, 2.1, and
        4.0
  

SUMMARY

You can iterate through all the MDI child windows in an MDI application without specifically activating them in turn. These CMDIChildWnd objects are managed by the MDIClient window, which covers the client area of the main frame window in an MDI application. Although this window does not have a corresponding MFC object, you can attach it to a CWnd object and use the features of the CWnd class to access each of the MDI child windows.

MORE INFORMATION

In MFC, each CMDIChildWnd created by the framework is managed as a child window of the MDIClient window. This MDIClient window is a child of the mainframe window and fills its client area. For MDI applications, the mainframe window is encapsulated by the CMDIFrameWnd class. This class has a public embedded HWND member (m_hWndMDIClient), which is the handle to the MDIClient window. For MDI applications, AppWizard derives the CMainFrame class from CMDIFrameWnd.

The MDIClient maintains an internal list of child windows. In an MFC application, these child windows are either a CMDIChildWnd object or an internal window used to display the title of an iconized window. Note that this is an internal list controlled by Windows; don't make assumptions about the ordering of children in the list after an API function is called.

How to Step Through the MDIClient's Child Window List

1. To access the MDIClient window in MFC, attach a CWnd derived class to m_hWndMDIClient as shown in the sample code. Another option is to subclass the MDIClient discussed in the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q103786

      TITLE     : Changing Window Background Color with Foundation Classes
   
   

2. Implement the GetNextMDIChildWnd() function as defined below. This custom member of the CMDIFrameWnd-derived object uses another custom member, m_pWndCurrentChild, to store the current child window between calls.

3. Implement the GetCountCMDIChildWnds() function as defined below. Another custom member of the CMDIFrameWnd-derived object, this function calls GetNextMDIChildWnd() to get the count of CMDIChildWnd objects maintained by the MDIClient.

Sample Code

//**mainfrm.h***************************************************

   CWnd  m_wndMDIClient;
   CWnd* m_pWndCurrentChild;
   CMDIChildWnd* GetNextMDIChildWnd();
   int GetCountCMDIChildWnds();

//**mainfrm.cpp**************************************************

  //.................

CMainFrame::~CMainFrame() {

  m_wndMDIClient.Detach();
  //.................

int CMainFrame::OnCreate(LPCREATESTRUCT lpCreateStruct)

  if (CMDIFrameWnd::OnCreate(lpCreateStruct) == -1)
    return -1;

    if (m_wndMDIClient.Attach(m_hWndMDIClient) == 0)
    {
        TRACE0("Failed to attach MDIClient.\n");
        return -1;      // fail to create
    }
  //.................

//----------------------------------------------------------------
// This function finds the CMDIChildWnd in the list of windows
// maintained by the application's MDIClient window following the
// one pointed to by the member variable m_pWndCurrentChild. If no
// further CMDIChildWnds are in the list, NULL is returned.
//----------------------------------------------------------------

   if (!m_pWndCurrentChild)
     {
      // Get the first child window.
      m_pWndCurrentChild = m_wndMDIClient.GetWindow(GW_CHILD);
     }
   else
     {
      // Get the next child window in the list.
        m_pWndCurrentChild=
           (CMDIChildWnd*)m_pWndCurrentChild->GetWindow(GW_HWNDNEXT);
     }

   if (!m_pWndCurrentChild)
     {
      // No child windows exist in the MDIClient,
      // or you are at the end of the list. This check
      // will terminate any recursion.
      return NULL;
     }

  // Check the kind of window
    if (!m_pWndCurrentChild->GetWindow(GW_OWNER))
      {
        if (m_pWndCurrentChild->
                           IsKindOf(RUNTIME_CLASS(CMDIChildWnd)))
          {
                 // CMDIChildWnd or a derived class.
                 return (CMDIChildWnd*)m_pWndCurrentChild;
          }
        else
          {
                 // Window is foreign to the MFC framework.
                 // Check the next window in the list recursively.
                 return GetNextMDIChildWnd();
          }
      }
    else
      {
          // Title window associated with an iconized child window.
          // Recurse over the window manager's list of windows.
          return GetNextMDIChildWnd();
      }

//-----------------------------------------------------------------
// This function counts the number of CMDIChildWnd objects
// currently maintained by the MDIClient.
//-----------------------------------------------------------------

int CMainFrame::GetCountCMDIChildWnds()

 int count = 0;

 CMDIChildWnd* pChild = GetNextMDIChildWnd();
 while (pChild)
  {
    count++;
    pChild = GetNextMDIChildWnd();
  }
 return count;