Running only 1 instance

Good Morning !

I need to run only 1 instance of my application.

I'm betting I need to use app.PrevInstance. But it seems that I can't make it work... I guess I need to know which application is running..

Any help would be appreciated thanks

Nicolas

You can use App.PrevInstance. But from my experience sometimes it is not very stable. For example when you kill the second instance of the app and check the task list you might still have your app running there.
I prefer to use API. Here is an example

'module declarations
Public Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Public Declare Function PostMessage Lib "user32" Alias "PostMessageA" _
(ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, ByVal lParam As Long) As Long


'Constants used by the API functions
Public Const WM_CLOSE = &H10

'in the form

Private Sub Form_Load()
'========================================================================
If App.PrevInstance Then KillSecondApp
End Sub

Private Sub KillSecondApp()
'=============================================================================
Dim hWindow As Long
Dim lngReturnValue As Long


hWindow = FindWindow(vbNullString, "Your Window Caption")
lngReturnValue = PostMessage(hWindow, WM_CLOSE, vbNull, vbNull)
End Sub

Iouri Boutchkine
[email protected]

Here is a simple prigram that enters into a TextBox all available runnning programs.
Start a new project. Add a textbox to the form.
Add a module
paste this code into the appropriate spot.

' In the form
'
option Explicit

'Add this code to a form
private Sub Form_Load()
'KPD-Team 2000
'URL: http://www.allapi.net/
'E-Mail: [email protected]
'set the form's graphics mode to persistent
me.AutoRedraw = true
'call the Enumwindows-function
Dim x
EnumWindows AddressOf EnumWindowsProc, byval 0&
End Sub
'
'
' In the module
'
option Explicit
'KPD-Team 2000
'URL: http://www.allapi.net/
'E-Mail: [email protected]

'Add this code to a module
Declare Function EnumWindows Lib "user32" (byval lpEnumFunc as Long, byval lParam as Long) as Boolean
Declare Function GetWindowText Lib "user32" Alias "GetWindowTextA" (byval hwnd as Long, byval lpString as string, byval cch as Long) as Long
Declare Function GetWindowTextLength Lib "user32" Alias "GetWindowTextLengthA" (byval hwnd as Long) as Long
public Function EnumWindowsProc(byval hwnd as Long, byval lParam as Long) as string
Dim sSave as string, Ret as Long
Ret = GetWindowTextLength(hwnd)
sSave = Space(Ret)
GetWindowText hwnd, sSave, Ret + 1
If Trim(sSave) <> "" then _
frmIsMeRunning.Text1 = frmIsMeRunning.Text1 & sSave & vbCrLf
'continue enumeration
EnumWindowsProc = true
End Function




'
Run the program. Use its output to compare against your app name.

John G

If I do this it is working but I'm getting a run-time error so It might be this.. I'm not sure

I'm using this

if App.PrevInstance then
end
end if

But I'm getting the run-time error only on Winnt with 1 instance started

It says that

The instruction at 0x70223EFF referenced memory at 0x70223EFF. The memory could not be "Read".

And the worse is that my application is working great till you try to close it, it says that once in a while.. Need to find it GRR.

Sigh :(

Nicolas

For the App.PrevInstance property to be true the same application should be invoked from either the application Full Path or shortcuts. Invoking a copy of the application will not fire the App PrevInstance. The code below should do what you asked for.
private Sub Form_Load()
If App.PrevInstance then
'Delete the following line after testing
MsgBox "Found Instance"
Unload me
End
End If
End Sub