ACC: Determining How Many Instances of Application Are Active (167843)

MORE INFORMATION

1. Start Microsoft Access and create a new, blank database called TestAPI.mdb.
2. Create a module and type the following lines in the Declarations section:

         '------------------------------------------
         ' Global Declarations Section Of The Module
         '------------------------------------------
   
   
         Declare Function GetWindow Lib "user32" (ByVal hwnd As Long, _
         ByVal wCmd As Long) As Long
   
         Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" _
         (ByVal hwnd As Long, ByVal lpString As String, ByVal CCh As Long) _
         As Long
   
         Declare Function IsWindowVisible Lib "user32" (ByVal hwnd As Long) _
         As Long
   
         Public Const GW_HWNDFIRST = 0
         Public Const GW_HWNDLAST  = 1
         Public Const GW_HWNDNEXT  = 2
         Public Const GW_HWNDPREV  = 3
   					

3. Type the following procedures:

         ' This function returns the Caption Text of each window passed to
         ' it. If a window does not have a Caption bar, then this function
         ' returns a zero-length string ("")
   
         Function GetAppName(Lnghwnd as long)
            Dim LngResult As Long
            Dim StrWinText As String * 255
            Dim LngCCh As Long
            LngResult = GetWindowText(Lnghwnd, StrWinText, 255)
            GetAppName = Left(StrWinText, LngResult)
         End Function
   
         ' This function counts all instances of an application that are open,
         ' including any windows that are not visible.
         ' Arguments: LngHwnd        = Any valid window handle.
         '            StrAppCaption  = The window caption to search for.
         ' Example:   GetCountOfWindows(hWndAccessApp,"Microsoft Access")
         Function GetCountOfWindows(Lnghwnd, StrAppCaption)
            Dim LngResult As Long
            Dim LngICount As Long
            Dim StrAppName As String
   
            LngResult = GetWindow(Lnghwnd, GW_HWNDFIRST)
            Do Until LngResult = 0
               If IsWindowVisible(LngResult) Then
                  StrAppName = GetAppName(LngResult)
                  If InStr(1, StrAppName, StrAppCaption) Then
                     LngICount = LngICount + 1
                  End If
               End If
               LngResult = GetWindow(LngResult, GW_HWNDNEXT)
            Loop
            GetCountOfWindows = LngICount
            End Function
   					

4. Save the module as Module1 and close it.
5. Create a new form not based on any table or query in Design view.
6. Set the OnOpen property of the form to the following event procedure:

         Private Sub Form_Open(Cancel As Integer)
         If GetCountOfWindows(hWndAccessApp, "Microsoft Access") > 1 Then
            Cancel = True
            MsgBox "Please use the instance of Microsoft Access that is " _
                   & "already open."
            DoCmd.Quit acQuitSaveNone
         End If
         End Sub
   					

7. Save the form as frmStartup and close it.
8. On the Tools menu, click Startup.
9. In the Startup dialog box, select frmStartup in the Display Form box, and then click OK.
10. Close and then reopen the TestAPI database non-exclusively. Note that the frmStartup form appears.
11. Start another instance of Microsoft Access and open the TestAPI database. Note that you receive a message, and then the instance of Microsoft Access closes.