How to Prevent Mainframe Window from Being ReSized

WINDOWS        | WINDOWS NT

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with:

      - Microsoft Visual C++ for Windows, versions 1.5, 1.51, 1.52
      - Microsoft Visual C++, 32-bit Edition, versions 2.0, 2.1, 2.2,
        4.0, 4.1, 4.2
  

SUMMARY

Adding the WS_THICKFRAME windows style allows a window to be re-sized. By removing this from the Mainframe window's styles, you can prevent this window from being resized. Further, the MINMAXINFO structure stores the maximum and minimum tracking size of a window. The WM_GETMINMAXINFO message is sent to a window when the size or position of that window is about to change. An application can over-ride the handler for this message to set a window's default minimum or maximum tracking size.

MORE INFORMATION

You can prevent the Mainframe window of an AppWizard-generated SDI application from being resized by following these steps:

1. Modify the IDR_MAINFRAME menu to add a top-level menu item (F&reeze!) with an ID of ID_FREEZE.

2. Add a public Boolean data member (say, BOOL freezeState) to the CMainFrame class to keep track of the current state of the application. Initialize freezeState to FALSE in the constructor of the CMainFrame class.

3. Provide a command handler for the 'Freeze' menu item as follows:

      void CMainFrame::OnFreeze()
      {
         char* lpszFreeze = "F&reeze!";
         char* lpszUnFreeze = "&UnFreeze!";
         CMenu* pmenu = GetMenu();
         if (!freezeState)
         {
   
             freezeState = TRUE;
             pmenu->ModifyMenu(ID_FREEZE, MF_STRING, ID_FREEZE,
                                                          lpszUnFreeze);
             DWORD style = ::GetWindowLong(this->m_hWnd, GWL_STYLE);
   
      // Remove the thick frame style and the Minimize, Maximize buttons
           style &= ~(WS_MAXIMIZEBOX|WS_MINIMIZEBOX|WS_THICKFRAME);
           ::SetWindowLong(this->m_hWnd, GWL_STYLE, style);
      }
      else
      {
          freezeState = FALSE;
          pmenu->ModifyMenu(ID_FREEZE, MF_STRING, ID_FREEZE,
                                                         lpszFreeze);
          DWORD style = ::GetWindowLong(this->m_hWnd, GWL_STYLE);
   
      // Add the thick frame style and the Minimize, Maximize buttons
         style |= (WS_MAXIMIZEBOX|WS_MINIMIZEBOX|WS_THICKFRAME);
         ::SetWindowLong(this->m_hWnd, GWL_STYLE, style);
         }
         DrawMenuBar();
      }
   
   

4. Provide a handler for the WM_GETMINMAXINFO message as follows:

      void CMainFrame::OnGetMinMaxInfo(MINMAXINFO FAR* lpMMI)
      {
         if (freezeState)
         {
             RECT rc;
   
             GetWindowRect(&rc);
             lpMMI->ptMaxSize.x = rc.right - rc.left;
             lpMMI->ptMaxSize.y = rc.bottom - rc.top;
             lpMMI->ptMaxPosition.x = rc.left;
             lpMMI->ptMaxPosition.y = rc.top;
             lpMMI->ptMinTrackSize.x = rc.right - rc.left;
             lpMMI->ptMinTrackSize.y = rc.bottom - rc.top;
             lpMMI->ptMaxTrackSize.x = rc.right - rc.left;
             lpMMI->ptMaxTrackSize.y = rc.bottom - rc.top;
         }
   
         CFrameWnd::OnGetMinMaxInfo(lpMMI);
      }
   
   

5. If the mainframe is maximized, disable the Freeze menu option because there is no point in making the window non-resizable because a maximized window cannot be resized anyway:

      void CMainFrame::OnSize(UINT nType, int cx, int cy)
      {
         CFrameWnd::OnSize(nType, cx, cy);
         CMenu* pmenu = GetMenu();
   
         if (nType == SIZE_MAXIMIZED)
             pmenu->EnableMenuItem(ID_FREEZE, MF_DISABLED|MF_GRAYED);
         else
             pmenu->EnableMenuItem(ID_FREEZE, MF_ENABLED);
   
         DrawMenuBar();
      }