FIX: CFormView Does Not Change Child Positions on WM_MDINEXT

WINDOWS   | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes, included with:

      - Microsoft Visual C++ for Windows, versions 1.0, 1.5
      - Microsoft Visual C++, 32-bit Edition, version 1.0
  

SYMPTOMS

The child controls of a CFormView do not get their positions restored (they do not get scrolled) if the CFormView is activated using WM_MDINEXT (CTRL+F6 or CTRL+TAB). This behavior is true for any CScrollView window that contains child controls.

CAUSE

CTRL+F6 sends a WM_MDINEXT message to the MDIClient window. This message is handled by Windows. During the processing of the WM_MDINEXT message, Windows hides the MDIClient window temporarily. This in turn causes all child windows to be hidden. The problem with this is that child windows which are hidden are not moved when the ScrollWindow API function is called. (The ScrollWindow function is used by CScrollView to scroll its client area.) As a result, child windows are not moved during WM_MDINEXT processing.

RESOLUTION

Modify the MFC source code and re-build the libraries. To re-build the libraries, please follow the steps outlined in the section titled "How to Build Other Library Versions" in the Class Library User's Guide.

NOTE: If you are rebuilding the MFC DLL (for example, MFC250D.DLL), you should also rename the DLL. This is also mentioned in MFC TechNote #33.

The changes necessary are in the file VIEWSCRL.CPP. In this file you will find two calls to ScrollWindow -- one in the ScrollToDevicePosition function and other in the OnScrollBy function. Replace the call to ScrollWindow in each of these functions with the following code; note that the first two lines are different in each function:

  // In ScrollToDevicePosition use the following two lines :

        int xAmount = xOrig - ptDev.x;
        int yAmount = yOrig - ptDev.y;

  // In OnScrollBy use the following two lines:

        int xAmount = -(x-xOrig);
        int yAmount = -(y-yOrig);

  // The rest of the following replacement code is the same in
  // both functions:

        if (IsWindowVisible())
        {

           // When visible, let Windows do the scrolling

           ScrollWindow(xAmount, yAmount);
        }
        else
        {

           // Windows does not perform any scrolling if the window
           // is not visible.  This leaves child windows unscrolled.
           // To account for this oversight, the child windows are
           // moved directly instead.

           HWND hWndChild = ::GetWindow(m_hWnd, GW_CHILD);
           if (hWndChild != NULL)
           {
             for (; hWndChild != NULL;
                hWndChild = ::GetNextWindow(hWndChild, GW_HWNDNEXT))
             {
               CRect rect;
               ::GetWindowRect(hWndChild, &rect);
               ScreenToClient(&rect);
               ::SetWindowPos(hWndChild, NULL,
               rect.left+xAmount, rect.top+yAmount, 0, 0,
               SWP_NOSIZE|SWP_NOACTIVATE|SWP_NOZORDER);
             }
            }
          }

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of the article. This bug was corrected in The Microsoft Foundation Classes, version 3.0, included with Visual C++, 32-bit Edition, version 2.0.

MORE INFORMATION

Steps to Reproduce Problem

The problem can be verified with the VIEWEX sample.

1. Execute VIEWEX and choose File.New and select "Input Form View."

2. Shrink this child window until scroll bars appear.

3. Move the vertical scrollbar thumb to the bottom such that some of the controls are clipped at the top of the view.

4. Choose File.New and select "Simple Text."

5. Maximize this new child window.

6. Press CTRL+F6 to switch activation to the first child window -- the Input Form View.