Q238100: HOWTO: Limit 32-Bit MFC SDI App to a Single Instance in WinCE

Article: Q238100
Product(s): Microsoft C Compiler
Version(s): 5.0,6.0
Operating System(s): 
Keyword(s): kbMFC kbVC kbVC500 kbVC600 kbOSWinCEsearch kbDSupport kbGrpDSMFCATL
Last Modified: 13-MAY-2002

-------------------------------------------------------------------------------
The information in this article applies to:

- The Microsoft Foundation Classes (MFC), included with:
   - Microsoft Windows CE Toolkit for Visual C++, versions 5.0, 6.0 
-------------------------------------------------------------------------------

SUMMARY
=======

This article disscusses how to limit 32-bit applications to a single instance on
WinCE.

MORE INFORMATION
================

The reason the steps outlined in article Q141752 do not work for WinCE is
because, under WinCE, wce_PreCreateWindow function prefixes "WCE_" to class name
of the window. For example, if you register a class name of "MyNewClass", the
actual class name you need to pass to FindWindow() is "WCE_MyNewClass".

Sample code
-----------

1. Create a default WCE MFC AppWizard (exe)

2. Select the ClassView tab, and go to the definition of InitInstance in the
  Application class. Add the code at the begining of the definition of
  InitInstance:

     BOOL CSampleApp::InitInstance()
     {
     /********************************************************************/ 
      // If a previous instance of the application is already running,
      // then activate it and return FALSE from InitInstance to
      // end the execution of this instance.

      CWnd *pWndPrev;
   
      // Determine if another window with your class name exists...
      if (pWndPrev = CWnd::FindWindow(_T("WCE_MyNewClass"),NULL))
      {
          // Bring previous instance to the foreground
  	pWndPrev->SetForegroundWindow();
  	return FALSE;
      }
      WNDCLASS wndcls;

      memset(&wndcls, 0, sizeof(WNDCLASS));   // start with NULL defaults

      wndcls.style = CS_DBLCLKS | CS_HREDRAW | CS_VREDRAW;
      wndcls.lpfnWndProc = ::DefWindowProc;
      wndcls.hInstance = AfxGetInstanceHandle();
      wndcls.hIcon = LoadIcon(IDR_MAINFRAME); // or load a different icon
      wndcls.hbrBackground = (HBRUSH) (COLOR_WINDOW + 1);
      wndcls.lpszMenuName = NULL;
      // Specify your own class name for using FindWindow later
      wndcls.lpszClassName = _T("MyNewClass");

      // Register the new class and exit if it fails
      if(!AfxRegisterClass(&wndcls))
      {
         AfxMessageBox(_T("Class Registration Failed\n"));
         return FALSE;
      }
     /********************************************************************/ 
     // Other code here...
     }

3. Find the definition of PreCreateWindow for the Main Frame and add the
  following code.

     BOOL CMainFrame::PreCreateWindow(CREATESTRUCT& cs)
     {
       if( !CFrameWnd::PreCreateWindow(cs) )
  	return FALSE;
     /*************************************/ 
       cs.lpszClass = _T("MyNewClass");
     /*************************************/ 
       return TRUE;
     }

4. Right-click CSampleApp and add a Virtual Function ExitInstance. Add the
  following code in the function body:

     int CSampleApp::ExitInstance() 
     {
      // Add your specialized code here and/or call the base class
     /*********************/ 
      ::UnregisterClass(_T("MyNewClass"),AfxGetInstanceHandle());
     /*********************/        	
      return CWinApp::ExitInstance();
     }

5. Choose your target, select Rebuild All and then select Run.

REFERENCES
==========

  Q141752 SAMPLE: Limiting 32-bit Applications to a Single Instance

(c) Microsoft Corporation 1999, All Rights Reserved.
Contributions by Vidyanand Rajpathak, Microsoft Corporation


Additional query words: VCCE, single, Instance

======================================================================
Keywords          : kbMFC kbVC kbVC500 kbVC600 kbOSWinCEsearch kbDSupport kbGrpDSMFCATL 
Technology        : kbAudDeveloper kbMFC
Version           : :5.0,6.0
Issue type        : kbhowto

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1986-2002.