Microsoft KB Archive/88167

= ACC: How to Determine If a Specific Windows Program Is Running =

Article ID: 88167

Article Last Modified on 1/18/2007

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APPLIES TO


 * Microsoft Access 2.0 Standard Edition
 * Microsoft Access 95 Standard Edition
 * Microsoft Access 97 Standard Edition

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This article was previously published under Q88167



Advanced: Requires expert coding, interoperability, and multiuser skills.



SUMMARY
There may be times when you want only one instance of an application to run under Microsoft Windows. For example, if you add a command button to a form that starts the Windows Calculator (Calc.exe) program, the user can start many instances of Calculator. This is an inefficient use of memory and system resources. Through the use of a Windows application programming interface (API) function, Microsoft Access can determine if Calculator is already running.

The API function used to determine if a specific program is running is called FindWindow. FindWindow returns the handle of the window whose class is given by the lpClassName parameter and whose window name (or caption) is given by the lpCaption parameter. If the returned value is zero, the application is not running.

This article assumes that you are familiar with Visual Basic for Applications and with creating Microsoft Access applications using the programming tools provided with Microsoft Access. For more information about Visual Basic for Applications, please refer to your version of the &quot;Building Applications with Microsoft Access&quot; manual.

NOTE: Visual Basic for Applications is called Access Basic in Microsoft Access version 2.0. For more information about Access Basic, please refer to the &quot;Building Applications&quot; manual.



MORE INFORMATION
When a program is started from an icon or the command line, it registers the class name of its main window. The window class provides information about the name, attributes, and resources required by the program. The Microsoft Access window has a class name of &quot;OMain.&quot; Additional command class names are provided at the end of this article.

By calling FindWindow with a combination of a specific program's class name or the title bar caption, Microsoft Access can determine whether that specific program is running.

You can determine the class name of an application by using Spy.exe, which is supplied with the Microsoft Windows Software Development Kit (SDK) version 3.1. or the Microsoft Win32 SDK.

If the window has a caption bar title, you can also use the title to locate the instance of the running application. This caption text is valid even when the application is minimized to an icon.

The following example shows three ways to determine if the Windows Calculator is running.

NOTE: You may have some Microsoft Windows API functions defined in an existing Microsoft Access library; therefore, your declarations may be duplicates. If you receive a duplicate procedure name error message, remove or comment out the declarations statement in your code.

  Create a module and type the following line in the Declarations section.

NOTE: In the following sample code, an underscore (_) at the end of a line is used as a line-continuation character. Remove the underscore from the end of the line when re-creating this code in Access Basic.In version 7.0 and 97: Option Explicit

Declare Function FindWindow Lib &quot;user32&quot; Alias &quot;FindWindowA&quot; (_                      ByVal lpClassName as Any,_                       ByVal lpWindowName as Any) As Long In version 2.0: Option Explicit Declare Function FindWindow% Lib &quot;user&quot; (_                      ByVal lpClassName As Any,_                       ByVal lpCaption As Any)   Type the following procedure: Function CalculatorUp

Const lpClassName = &quot;SciCalc&quot; Const lpCaption = &quot;Calculator&quot;

'This demonstrates three different ways to call FindWindow: '1. The ClassName only. '2. The Caption only. '3. Both the ClassName and the Caption 'NOTE: When using Access 2.0, the value 0& must be used to           '      pass a null string to the FindWindow function rather '     than the constant VBNullString. For Example: '     FindWindow(lpClassName, 0&)

MsgBox &quot;Calculator Handle = &quot; & FindWindow(lpClassName, _              VBNullString) MsgBox &quot;Calculator Handle = &quot; & FindWindow(VBNullString, _              lpCaption) MsgBox &quot;Calculator Handle = &quot; & FindWindow(lpClassName, _              lpCaption)

'This function could return the handle of a window. CalculatorUp = FindWindow(lpClassName, 0&) End Function   To test this function, start Calculator, type the following line in the Debug window (or Immediate window in version 2.0), and then press ENTER: ?CalculatorUp Note that three message boxes open, each displaying the handle to the Calculator window. If Calculator is not running, each message box will display a zero. 

Below are some class names of some common Windows applications:   Class Name         Application ---

SciCalc           CALC.EXE CalWndMain        CALENDAR.EXE Cardfile          CARDFILE.EXE Clipboard         CLIPBOARD.EXE Clock             CLOCK.EXE CtlPanelClass     CONTROL.EXE XLMain            EXCEL.EXE Session           MS-DOS.EXE Notepad           NOTEPAD.EXE pbParent          PBRUSH.EXE Pif               PIFEDIT.EXE PrintManager      PRINTMAN.EXE Progman           PROGMAN.EXE   (Windows Program Manager) Recorder          RECORDER.EXE Reversi           REVERSI.EXE #32770            SETUP.EXE Solitaire         SOL.EXE Terminal          TERMINAL.EXE WFS_Frame         WINFILE.EXE MW_WINHELP        WINHELP.EXE #32770            WINVER.EXE OpusApp           WINWORD.EXE MSWRITE_MENU      WRITE.EXE   Windows 95 Only:

MSPaintApp        PBRUSH.EXE ExploreWClass     EXPLORER.EXE WordPadClass      WORDPAD.EXE

