Preventing more than one instance of app running

Hi there

Is there any way to prevent more than one instance of one's application to run at the same time? Is there any way to check when the application loads if an instance of the app is already running and if it is then don't load the application?

Microsoft seems to do this with Office applications.

Many thanks

langals

In your SubMain or Form_Load....

VB Code:

If App.PrevInstance = True Then
    MsgBox "Application is already running..."
    End
End If

Quote:

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Originally Posted by langals

Hi there

Is there any way to prevent more than one instance of one's application to run at the same time? Is there any way to check when the application loads if an instance of the app is already running and if it is then don't load the application?

Microsoft seems to do this with Office applications.

Many thanks

langals

---

Try something like this:

VB Code:

Private Sub Form_Load()
    Dim frmMyForm As Form
    If App.PrevInstance = True Then
        For Each frmMyForm In Forms
            Unload frmMyForm
            Set frmMyForm = Nothing
        Next frmMyForm
        Set frmMyForm = Nothing
        End
    End If
End Sub

Cheers,

RyanJ

Quote:

---

Originally Posted by sciguyryan

Private Sub Form_Load()
Dim frmMyForm As Form
If App.PrevInstance = True Then
For Each frmMyForm In Forms
Unload frmMyForm
Set frmMyForm = Nothing
Next frmMyForm
Set frmMyForm = Nothing
End
End If
End Sub

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I think the bold ones are unnecessary since the app is still loading, thus I assume no form has been loaded yet......

Quote:

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Originally Posted by dee-u

I think the bold ones are unnecessary since the app is still loading, thus I assume no form has been loaded yet......

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Probably but I always leave them there just to be shure. Unless you are looking for a very snappy shutdown (Which that code will not affect by much in any case) it should work all the same :)

Cheers,

RyanJ

Try also this link.

Quote:

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Originally Posted by dee-u

Try also this link.

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Nice use of a mutex there. I'd say that's probably the best way to do it, out of the ways I've seen so far (registry flag etc.).

If your app is one that loads data (like a document reader), just quitting if there is an existing instance probably isn't enough. Every time you open a Word document from Explorer, you are opening an instance of Word. If there is already an instance, it sends the document path back to the original instance before it quits, otherwise the document would never get opened. There are a variety of ways you can do this. One way (probably the simplest) is shown in the "Sending strings between VB apps" link in my sig.

Thanks for the help guys - that did the trick.

langals

This alternative might be noteworthy too....

VB Code:

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Public Sub Main()
    Dim m_hWnd As Long
 
    'Change Form1 to your form Caption.
    m_hWnd = FindWindow(vbNullString, "Form1")
    If m_hWnd > 0 Then
        MsgBox "Program " & App.Title & " is already running..."
        Unload Form1
        Exit Sub
    End If
 
    'Change Form1 to your form name.
    Form1.Show
End Sub

Quote:

---

Originally Posted by dee-u

This alternative might be noteworthy too....

VB Code:

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long
Public Sub Main()
    Dim m_hWnd As Long
 
    'Change Form1 to your form Caption.
    m_hWnd = FindWindow(vbNullString, "Form1")
    If m_hWnd > 0 Then
        MsgBox "Program " & App.Title & " is already running..."
        Unload Form1
        Exit Sub
    End If
 
    'Change Form1 to your form name.
    Form1.Show
End Sub

---

I am trying to use your code with a login form, the prompt comes up to say its already loaded but it also logs you in without credentials... ugh.

VB Code:

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" _
(ByVal lpClassName As String, ByVal lpWindowName As String) As Long
 
Public Sub Main()
    Dim m_hWnd As Long
 
    'Change Form1 to your form Caption.
    m_hWnd = FindWindow(vbNullString, "Login to Client Manager Pro")
    If m_hWnd > 0 Then
        frmAppAlreadyRunning.Show vbModal
        Unload frmLoginForm
        Exit Sub
    Else
        frmLoginForm.Show
    End If
End Sub

Put it in sub Main before the frmLogin ever gets called.

Quote:

---

Originally Posted by dglienna

Put it in sub Main before the frmLogin ever gets called.

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tried that too and when you click on the desktop icon. nothing loads, nothing checks, nothing happens.

This only runs the code if it's registered, and doesn't allow it to be executed twice. It is a case that you have to use END.

Post the code that you have. Sounds like the app is still running in the background.

VB Code:

Public Sub Main()
    If App.PrevInstance Then
     Beep
     End
    Else
      GetAppEnvironment
      If Not gRegClass.Registered Then
        frmRegister.Show vbModal
        End
      Else
        frmBackground.Show
      End If
    End If
End Sub

Quote:

---

Originally Posted by dglienna

This only runs the code if it's registered, and doesn't allow it to be executed twice. It is a case that you have to use END.

Post the code that you have. Sounds like the app is still running in the background.

VB Code:

Public Sub Main()
    If App.PrevInstance Then
     Beep
     End
    Else
      GetAppEnvironment
      If Not gRegClass.Registered Then
        frmRegister.Show vbModal
        End
      Else
        frmBackground.Show
      End If
    End If
End Sub

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ill try it and get back to you :)