PRB: Control Bar Not Visible After Calling Create

• The Microsoft Foundation Classes (MFC), included 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 2.0, 2.1, 4.0

SYMPTOMS

A control bar is not immediately visible after a call to Create. The control bar becomes visible only when the parent window is resized (or minimized\maximized). This behavior is true for all the built-in framework classes derived from CControlBar:

   CDialogBar
   CToolBar
   CStatusBar 

CAUSE

A control bar is initially placed at position (0,0) with size (0,0) so that the parent frame can control the size and position. The size and position are recomputed when a call is made to RecalcLayout. If a call is made to Create, then the control bar will not become visible until RecalcLayout is called for the parent frame window. The control bar becomes visible when the main frame window is resized, because CFrameWnd has a WM_SIZE handler that calls RecalcLayout.

RESOLUTION

Use one of the following to resolve this issue:

• If the control bar is ALWAYS going to be attached to the frame window when it is created, then create the control bar once in the OnCreate message handler for the frame window. This would apply to the main frame window of an SDI (CFrameWnd) or MDI (CMDIFrameWnd) application, or to an MDI Child Window (CMDIChildWnd).



• If the control is to be created dynamically (for example, a toolbar that pops-up only under certain circumstances), make a call to RecalcLayout for the parent frame window to cause the control bar to be properly resized and drawn.

MORE INFORMATION

There are two code segments below that show how to create a CDialogBar attached to a CMDIChildWnd. The first sample creates a CDialogBar as soon as the child window is created (that is, the child window always has the dialog bar). The second sample shows a function that will properly create and display a dialog bar at any time.

Sample Code

   /* Compile options needed: None
      Sample 1 - Override OnCreate.
   
      Note that the dialog template is called IDD_CHILDBAR
      and that CMyMDIChild has a member variable declaration:
      CDialogBar m_dlgbar;
   */ 
   int CMyMDIChild::OnCreate(LPCREATESTRUCT lpCreateStruct)
   {
        if (CMDIChildWnd::OnCreate(lpCreateStruct) == -1)
             return -1;
   
       m_dlgbar.Create(this,IDD_CHILDBAR,CBRS_TOP,115);
   
        return 0;
   }
   
   /*
     Sample 2 - Creating a dialog bar at any time.
     Note that the dialog template is called IDD_CHILDBAR
     and that CMyMDIChildWnd has a member variable declaration:
     CDialogBar *m_pdlgbar;
   */ 
   void CMyMDIChild::CreateDialogBar()
   {
       m_pDlgBar = new CDialogBar();
       m_pDlgBar->Create(this,IDD_CHILDBAR,CBRS_TOP,115);
       RecalcLayout();
   } 

Additional query words: WM_SIZE CRect tool bar status tool-bar status-bar statusbar

Keywords : kbMFC KbUIDesign kbVC
Version : 1.00 1.50 1.51 1.52 2.0 2.1 4.0
Platform : NT WINDOWS
Issue type :