FIX: CSplitterWnd Class Does Not Handle All Focus Cases

RESOLUTION

Microsoft has confirmed this to be a problem in the Microsoft Foundation Class (MFC) Libraries version 2.0. This problem has been fixed in the MFC Libraries version 2.5, which is included in Visual C++ version 1.5 for Windows. In the fixed code, CSplitterWnd::StopTracking() (in WINSPLIT.CPP) is modified to explicitly set the focus even after calling SetActiveView(). The code is:

   if (pOldActiveView == pParent->GetActiveView())
      {
          pParent->SetActiveView(pOldActiveView); // Re-activate.
          if (pOldActiveView != NULL)
              pOldActiveView->SetFocus(); // Make sure focus is restored.
      }
				

You can include this fix into WINSPLIT.CPP and then rebuild the MFC library by following the directions in Appendix B of the "Class Libraries User's Guide" as well as the README.TXT file located in the \MSVC\MFC\SRC directory.

Another workaround for the bug is to save and restore the keyboard focus throughout the splitter window's tracking process. This can be done by handling the WM_LBUTTONDOWN and WM_LBUTTONUP messages in the CSplitterWnd class. The following code demonstrates how to accomplish this:

   class CMySplit:public CSplitterWnd    // derive from it.
   {
       public:
       // This is the pointer to the window that
       // has focus when the splitter starts resizing.
       HWND hWndFocus;

       // ...rest of your declaration.
   }

   void CMySplit::OnLButtonDown(UINT nFlags, CPoint point)
   {
       //Get CWnd with current focus
       hWndFocus = ::GetFocus();

       // Remember to call the base class handler.
       CSplitterWnd::OnLButtonDown(nFlags,point);
   }

   void CMySplit::OnLButtonUp(UINT nFlags, CPoint point)
   {
       //restore focus
       ::SetFocus(hWndFocus);

       // Remember to call the base class handler.
       CSplitterWnd::OnLButtonUp(nFlags,point);
   }
				

The code above assumes that the focus is being set to one of the windows in the splitter window panes before the OnLButtonDown() handler is called. That is, you probably wouldn't want to set the focus back to some other window outside of the splitter window when the mouse button is released. You could write additional code to check to see if the focus is set to a window in one of the panes by checking the splitter's frame window's m_pActiveView variable.