Article: Q131994
Product(s): Microsoft C Compiler
Version(s): winnt:1.0,2.0,2.1,4.0
Operating System(s):
Keyword(s): kbDocView kbMDI kbMFC kbVC kbGrpDSMFCATL
Last Modified: 29-JUL-2001
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The information in this article applies to:
- The Microsoft Foundation Classes (MFC), used 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
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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:
Q103786 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.
NOTE: You can derive a class from CMDIChildWnd to customize the behavior of the
MDI child windows in your application. For example, you can add information to
further differentiate between the CMDIChildWnd derived classes.
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;
}
Additional query words: kbinf 1.00 1.50 1.10 2.00 2.10 2.50 2.51 2.52 3.10 4.00
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Keywords : kbDocView kbMDI kbMFC kbVC kbGrpDSMFCATL
Technology : kbAudDeveloper kbMFC
Version : winnt:1.0,2.0,2.1,4.0
Issue type : kbhowto
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