When If App.PrevInstance doesn't detect a previous instance

I've found this code in this forum

Private sub Form_Load()
'see if there is an istance already
If App.PrevInstance Then
msgbox "Application is already running"
AppActivate App.Title
'send the key (here SHIFT key) to set the form from the Prev Instance to the top
SendKeys "+", True

'Terminate the new instance
Unload Me
End if
End sub

However, It doesn't appear to work for me.
(I don't care about the SendKeys() and AppActivate() calls, so I'm down to this)

Private sub Form_Load()
'see if there is an istance already
If App.PrevInstance Then
'Terminate the new instance
Unload Me
End if
End sub



I've tried running this


If App.PrevInstance Then
'Terminate the new instance
Exit Sub
End if


as the first line of code in my main() routine as well, and it just does not detect another instance of the program running.

What would cause this ?

did you put the code in sub main ? have you set the startup object to sub main ? there is no problem with app.previnstance.

If you have the app running inside the IDE it won't pick up the prevInstance.

If you make a copy of the exe in a different folder, and launch the two copy of same exe, they will not know of each other)
Or even if you make a copy of exe in same foder (with a different filename name) and run, they will not know they are the same...

Also keep in mind that Windows NT can support multiple desktops and if you use an exe designed to work with distributed COM, even more funky stuff can occur.

Quote:

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Originally posted by Cimperiali
If you make a copy of the exe in a different folder, and launch the two copy of same exe, they will not know of each other)
Or even if you make a copy of exe in same foder (with a different filename name) and run, they will not know they are the same...

---

So what needs to be done to make this mechanism work ?

Quote:

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Originally posted by hendramin
did you put the code in sub main ? have you set the startup object to sub main ? there is no problem with app.previnstance.

---

As posted in my original message, I have tried this as the first few lines in main(), as well as in form_load() of the first form which is loaded.

No matter what I've tried, it doens't seem to work- so obviously, I'm missing something crucial :-)

Quote:

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Originally posted by Twodogs
If you have the app running inside the IDE it won't pick up the prevInstance.

---

I had originally tried it inside of the IDE, but then I compiled 2 identical EXE's, with different filenames.

When I run those 2 exe's, they still run as if the App.Previnstance code is not even there, so obviously I am doing somehting wrong

Quote:

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Originally posted by hendramin
did you put the code in sub main ? have you set the startup object to sub main ? there is no problem with app.previnstance.

---

Hmm. I'm not sure how to explicitly set the "startup object to sub main", but main() is called before any of the formas (as verified with a breakpoint). Maybe this is the default??

How does one explicitly set main() to be called as the startup objec t?

Quote:

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How does one explicitly set main() to be called as the startup objec t?

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Go to Project>>Project Properties>>General>>Startup Object and set to Sub Main

Have you stepped though the code to see if in fact the .previnstance is false?

Quote:

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Originally posted by Cimperiali
If you make a copy of the exe in a different folder, and launch the two copy of same exe, they will not know of each other)
Or even if you make a copy of exe in same foder (with a different filename name) and run, they will not know they are the same...

---

I did not realize this before !!
seems that PrevInstance checks if the EXE module is loaded or not..
So this does not work if you make copies of the EXE

anyway this is my solution for this prolem :

clsMutex Code :

Code:

---

Option Explicit

Private Declare Function CreateMutex Lib "kernel32" Alias "CreateMutexA" (lpMutexAttributes As SECURITY_ATTRIBUTES, ByVal bInitialOwner As Long, ByVal lpName As String) As Long
Private Declare Function CloseHandle Lib "kernel32" (ByVal hObject As Long) As Long

Private Type SECURITY_ATTRIBUTES
    nLength As Long
    lpSecurityDescriptor As Long
    bInheritHandle As Long
End Type

Private Const ERROR_ALREADY_EXISTS = 183&

Private m_hMutex As Long

Public Function CheckMutex(MutexName As String) As Boolean

Dim s As SECURITY_ATTRIBUTES
m_hMutex = CreateMutex(s, 0, MutexName)

If Err.LastDllError = ERROR_ALREADY_EXISTS Then
    CheckMutex = False
Else
    CheckMutex = True
End If

End Function


Private Sub Class_Terminate()
CloseHandle m_hMutex
End Sub

---

Form code:

Code:

---

Option Explicit
Dim mut As clsMutex

Private Sub Form_Load()
Set mut = New clsMutex
If Not mut.CheckMutex("CodeGuru") Then 'Case sensitive string
    MsgBox "Application is running"
    Unload Me
End If

End Sub

---

How does it work ?
it creates a mutex (shared object that hace a uniqe name)..
if you try to recreate it you get the error :ERROR_ALREADY_EXISTS
this is the whole idea..But remember that mut (the clsMutex instance) must be alive as long as you application is still running because the mutex is close in the terminate event.
try it :)

Quote:

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Originally posted by cappy2112
but then I compiled 2 identical EXE's, with different filenames.

---

App.PrevInstance will look to see if the actual application is already running - not whether you have another exe running at the same time. ie - 2 copies of the same program running.

Quote:

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Originally posted by rocket
Go to Project>>Project Properties>>General>>Startup Object and set to Sub Main

Have you stepped though the code to see if in fact the .previnstance is false?

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yes- but it was because I was trying to run 2 copies (2 exe's) of the same program.

Now I'll have to try this again- the right way :-)

Quote:

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Originally posted by rocket
Go to Project>>Project Properties>>General>>Startup Object and set to Sub Main

Have you stepped though the code to see if in fact the .previnstance is false?

---

Very useful. I didn't use this before.

Quote:

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Originally posted by Twodogs
App.PrevInstance will look to see if the actual application is already running - not whether you have another exe running at the same time. ie - 2 copies of the same program running.

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Ok- App.Previnstance works for me now !!

thanks everyone!!

Quote:

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Originally posted by hspc
anyway this is my solution for this prolem :
[....]

How does it work ?
it creates a mutex (shared object that hace a uniqe name)..
if you try to recreate it you get the error :
ERROR_ALREADY_EXISTS
this is the whole idea...

---

I like your solution.

Another way (not this good, however)
is to have a check in sub main for a particular form
(FindWindow api will find it even if it is not visible)
you load and do not show. If you find it, program is
already running, if not, it is first instance
ie attached code

But your solution is better...
:)

Cimperiali..
thank you for the nice comment :)

If anyone is interested, here is my solution to PreviousInstance : DDE or LinkItem as VB call it.

On the main form, have these properties set :
LinkMode : 1 - Source
LinkTopic : "AppLinkTopic" [Can be anything]

Then on my Form Load using an invisible textbox I named TxtDDE :

Code:

---

TxtDDE.LinkMode = 0 ' None
TxtDDE.LinkTopic = "YourApplicationTitleHere|AppLinkTopic"
On Error goto NoDDE
TxtDDE.LinkMode = 2 ' Manual - Link to existing dde host
TxtDDE.LinkExecute "SHOWUP" ' When host receive this, it should activate itself
Unload Me
End

NoDDE:
' Continu loading here.

---

Here is the code I use to deal with the SHOWUP command (on the main form) :

Code:

---

Private Sub Form_LinkExecute(CmdStr As String, Cancel As Integer)
  If (UCase(CmdStr) = "SHOWUP") Then
    FrmMain.Visible = True
    FrmMain.WindowState = vbNormal
    FrmMain.SetFocus
  End If
  ' I use the same method to notify my application to quit ( for updates )
  If (UCase(CmdStr) = "QUIT") Then FrmLoad.Menu_TrayQuit_Click
End Sub

---

this works for me but only shows a message:

If App.PrevInstance Then
MsgBox "Application is already running"

n i need to load the previnstance, here's the code for getting the program to the taskbar:

Private Sub Form_Resize()

If Me.WindowState = 1 Then
'The user has minimized his window

Call Shell_NotifyIcon(NIM_ADD, IconData)

' Add the form's icon to the tray

Me.Hide

' Hide the button at the taskbar

End If

End Sub

Private Sub Form_Load()

With IconData

.cbSize = Len(IconData)
' The length of the NOTIFYICONDATA type

.hIcon = Me.Icon
' A reference to the form's icon

.hwnd = Me.hwnd
' hWnd of the form

.szTip = "Cyber-Net Lite" & Chr(0)
' Tooltip string delimited with a null character

.uCallbackMessage = WM_MOUSEMOVE
' The icon we're placing will send messages to the MouseMove event

.uFlags = NIF_ICON Or NIF_TIP Or NIF_MESSAGE
' It will have message handling and a tooltip

.uID = vbNull
' uID is not used by VB, so it's set to a Null value

End With

End Sub

Private Sub mnuExit_Click()

Unload Me
' Unload the form

End
' Just to be sure the program has ended

End Sub

Private Sub mnuShow_Click()

Me.WindowState = vbNormal
Shell_NotifyIcon NIM_DELETE, IconData
Me.Show

End Sub
Private Sub Form_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)

Dim msg As Long

msg = X
' The message is passed to the X value

' You must set your form's ScaleMode property to pixels in order to get the correct message

If msg = WM_LBUTTONDBLCLK Then
' The user has double-clicked your icon

Call mnuShow_Click
' Show the window

ElseIf msg = WM_RBUTTONDOWN Then
' Right-click

PopupMenu mnuPopup
' Popup the menu

End If

End Sub

Private Sub Form_Unload(Cancel As Integer)
Shell_NotifyIcon NIM_DELETE, IconData
Cancel = -1
End Sub

Can anybody please help me?

thnx