DOCUMENT:Q109059  30-JUL-1999  [foxpro]
TITLE   :HOWTO: Prevent Multiple Instances of an Application
PRODUCT :Microsoft FoxPro
PROD/VER:
OPER/SYS:
KEYWORDS:kbcode kbinterop kbvfp300 kbvfp500

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

 - Microsoft Visual FoxPro for Windows, versions 3.0, 5.0 
 - Microsoft FoxPro for Windows, versions 2.5x, 2.6x 
-------------------------------------------------------------------------------

SUMMARY
=======

The program shown below demonstrates how to stop a second instance of the same
FoxPro window from being started by using the Windows application programming
interface (API) function FindWindow() to test if a given window name already
exists. The FindWindow() function can be accessed by including FOXTOOLS.FLL, the
library file that is supplied with FoxPro for Windows and documented in the
Foxtools.hlp file.

NOTE: This method does not prevent multiple instances of FoxPro for Windows from
starting.

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

NOTE: This works in Windows for Workgroups 3.00, Windows 95, and Windows NT.

Copy this code into a program file in FoxPro for windows. The first time you call
the program, you will notice the main FoxPro window title change. The second
time you run it, you will get the message that you cannot start another instance
of the window.

NOTE: Set the window name after you check for its existence.

   

      SET LIBRARY TO SYS(2004)+"foxtools.fll" ADDITIVE
      * FindWindow() takes two parameters and returns the handle of the
      * window, HWND, if it was found.
      GetWind = RegFn("FindWindow", "CC", "I")
      *Set the first parameter of the call to getwind to 0, null.
      wclass=0
      winname="My Application"
      apphand=CallFn(GetWind,wclass ,winname)
      *If the call was successful, stop processing.
      IF apphand<>0
         WAIT WINDOW ;
           "You cannot start another instance of the window 'My Application'!"
         QUIT
      ENDIF
      MODIFY WINDOW screen TITLE "My Application"
      WAIT WINDOW ;
        "The first instance of the window 'My Application' is running."

REFERENCES
==========

Microsoft Windows Software Development Kit, "Programmer's Reference, Volume 2:
Functions," page 309

Foxtools.hlp, located in the C:\Vfp\Tools

Additional query words: foxtools sdk fll api recursive recursion loaded twice

======================================================================
Keywords          : kbcode kbinterop kbvfp300 kbvfp500 
Technology        : kbVFPsearch kbAudDeveloper kbFoxproSearch kbVFP300 kbVFP500
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 1999.