PRB: Setting First Pane of CStatusBar

• The Microsoft Foundation Classes (MFC) included with:

       - Microsoft Visual C++ 32-bit Edition, version 1.0, 2.0, 2.1, 4.0,
         4.1, 4.2, 5.0
       - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, 1.52
  

SYMPTOMS

If the text in the first pane of a CStatusBar window is changed using SetPaneText() and a menu is selected, the text is overwritten by the Help prompts for the menu.

CAUSE

Setting any but the first pane of the status bar is relatively simple. You just need to set the pane using SetPaneText() and make sure you have added in an ON_UPDATE_COMMAND_UI handler for the ID of that pane (set in your MAINFRAME.CPP as an element of an indicators[] array). This handler should call Enable() in the following manner to make sure that the pane is not erased:

   void CMainFrame::OnUpdateMystat(CCmdUI* pCmdUI)
   {
      pCmdUI->Enable();
   }

The problem is that the framework itself is changing the first pane using some special techniques. Basically, the framework is passing a WM_SETTEXT command directly to the status bar, from a number of places within its own code.

Adding ON_UPDATE_COMMAND_UI handlers or calling SetPaneText() for the first pane of the status bar does not permanently set it. The framework eventually sends a WM_SETTEXT message directly to the status bar, changing the text from what was set.

RESOLUTION

One way of setting the first pane yourself and keeping it set to what you want is to derive your own class from CStatusBar (for example CMyStat) and to give it a WM_SETTEXT handler. (Adding the WM_SETTEXT handler cannot be done using ClassWizard, so the handler must be added by hand.)

The steps to do this are as follows:

1. Use ClassWizard to add a new class, derived from a generic CWnd. Now edit the .H and .CPP files to change the two references to CWnd to CStatusBar.

2. Add a protected member function of CMyStat:

         afx_msg LRESULT OnSetText(WPARAM, LPARAM);
   

3. Add a message map entry for the function in the .CPP file, as follows:

         BEGIN_MESSAGE_MAP(CMyStat, CStatusBar)
            //{{AFX_MSG_MAP(CMyStat)
            // NOTE: ClassWizard will add and remove mapping macros here.
            //}}AFX_MSG_MAP
            ON_MESSAGE( WM_SETTEXT, OnSetText )
         END_MESSAGE_MAP()
   
   

4. Now implement the function as follows:

         LRESULT CMyStat::OnSetText(WPARAM wParam, LPARAM lParam)
         {
            if ( !bIgnoreSetText )
               return CStatusBar::OnSetText( wParam, lParam );
            return 0;  // Same as CStatusBar::OnSetText success
         }
   
      where bIgnoreSetText is true only if you have set your own text in the
      status bar with a SetPaneText() call.
   
   

5. Include CMyStat class header file in your MAINFRM.H file and replace:

         CStatusBar m_wndStatusBar;
   

       with the following:
   

          CMyStat     m_wndStatusBar;