BUG: Resizing CToolbar with Dropdown Arrow Buttons Freezes Apps

• The Microsoft Foundation Classes (MFC), included with:
  • Microsoft Visual C++, 32-bit Editions, version 6.0

SYMPTOMS

Resizing a toolbar (CToolBar class) with drop-down arrow buttons causes an infinite loop.

CAUSE

The application is looping in CToolBar::SizeToolBar() because neither sizeMin.cx nor sizeMax.cx changes its value. In other words, in CToolBar::SizeToolBar(), the loop hangs on the case where sizeMax == sizeMid.

RESOLUTION

Because CToolBar::SizeToolBar() is not a virtual function, we need to reimplement this function and override the virtual functions in CToolBar class to call our SizeToolBar() function.

Below are the steps to correct this problem:

1. Derive a class from CToolBar called CMyToolBar.



2. Override virtual functions: CalcFixedLayout() and CalcDynamicLayout() in CMyToolBar class because they both call CalcLayout(), which in turn calls SizeToolBar(). Both CalcLayout() and SizeToolBar are nonvirtual functions in CToolBar class.
   
   The code for all these functions can be copied from the MFC source file Bartool.cpp.



3. Override CalcLayout() in CMyToolBar class. The code in CToolBar::CalcLayout() requires the _AFX_CONTROLPOS structure, which should be copied from the Bartool.cpp file as well.
   
   The code in CToolBar::CalcLayout() also calls the _GetButton() and _SetButton() functions. These functions have internal linkage, so we need to override those to avoid the LNK2001 error.
   
   NOTE: The first statement of _GetButton() casts the "this" pointer to CToolBar*, we have to cast it to CMyToolBar* in order to call the protected CWnd::DefWindowProc() function. For example:

   
         void CMyToolBar::_GetButton(int nIndex, TBBUTTON* pButton) const
         {
            CMyToolBar* pBar = (CMyToolBar*) this;
            VERIFY(pBar->DefWindowProc(TB_GETBUTTON, nIndex,
              (LPARAM)pButton));
            // TBSTATE_ENABLED == TBBS_DISABLED so invert it.
            pButton->fsState ^= TBSTATE_ENABLED;
         } 




4. Override SizeToolBar() in CMyToolBar class. Replace the while-loop with the following fix-up code:

   
         while (sizeMin.cx < sizeMax.cx)
         {
            sizeMid.cx = (sizeMin.cx + sizeMax.cx) / 2;
            WrapToolBar(pData, nCount, sizeMid.cx);
            sizeMid = CalcSize(pData, nCount);
   
            if (nLength < sizeMid.cy)
            {
               if (sizeMin == sizeMid)
               {
                  WrapToolBar(pData, nCount, sizeMax.cx);
                  return;
               }
               sizeMin = sizeMid;
            }
            else if (nLength > sizeMid.cy && sizeMax != sizeMid)
               sizeMax = sizeMid;
            else
               return;
         } 




5. Finally, use CMyToolBar when declaring the toolbar object in the header file of the CMainFrame class.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article. We are researching this bug and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

In CToolBar::SizeToolBar(), the loop hangs on the case where sizeMax == sizeMid:

   while (sizeMin.cx < sizeMax.cx)
   {
      sizeMid.cx = (sizeMin.cx + sizeMax.cx) / 2;
      WrapToolBar(pData, nCount, sizeMid.cx);
      sizeMid = CalcSize(pData, nCount);

      if (nLength < sizeMid.cy)
      {
         if (sizeMin == sizeMid)
         {
            WrapToolBar(pData, nCount, sizeMax.cx);
            return;
         }
         sizeMin = sizeMid;
      }
      else if (nLength > sizeMid.cy)
         sizeMax = sizeMid;
      else
         return;
   } 

Steps to Reproduce Behavior

1. Run MFC AppWizard to create an SDI .EXE.



2. Add the following code to CMainFrame::OnCreate(), to add a drop-down arrow to the Open button:

   
         // Set the drop-down buttons to have the appropriate styles.
   
         CToolBarCtrl& rCtrl = m_wndToolBar.GetToolBarCtrl();
   
         TBBUTTONINFO tbbi;
         tbbi.dwMask = TBIF_STYLE;
         tbbi.cbSize = sizeof tbbi;
   
         rCtrl.GetButtonInfo(ID_FILE_OPEN, &tbbi);
         tbbi.fsStyle |= TBSTYLE_DROPDOWN;
   
         VERIFY(rCtrl.SetButtonInfo(ID_FILE_OPEN, &tbbi));
   
         rCtrl.SetExtendedStyle(
            rCtrl.GetExtendedStyle() | TBSTYLE_EX_DRAWDDARROWS); 




3. Build and run the .EXE.



4. Undock the toolbar.



5. Grab the BOTTOM border and resize, making the toolbar three rows in height (resizing using the right border seems to work fine).

© Microsoft Corporation 1998, All Rights Reserved.
Contributions by Yeong-Kah Tam, Microsoft Corporation

Additional query words: kbvc600bug

Keywords : kbVC600bug
Version : WINNT:6.0
Platform : winnt
Issue type : kbbug