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

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:

   103786 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***************************************************
class CMainFrame : public CMDIFrameWnd
{
...
public:
   CWnd  m_wndMDIClient;
   CWnd* m_pWndCurrentChild;
   CMDIChildWnd* GetNextMDIChildWnd();
   int GetCountCMDIChildWnds();
...
}

//**mainfrm.cpp**************************************************
CMainFrame::CMainFrame():m_pWndCurrentChild(NULL)
{
  //.................
}

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.
//----------------------------------------------------------------

CMDIChildWnd* CMainFrame::GetNextMDIChildWnd()
{
   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;
}