VB Question

Steve Meisel · Jun 28, 2007

Is there a way with VB6 to have the application check to see if there is another occurrance of the same application running?

We have several machines that are pc control, from VB, and when there are two of the same applications running strange things happen. Mostly the machine crashes and I stay busy for the next couple of hours.

I have talked to the programmer (outside contractor) but he is not sure how to make the check. Any ideas?

Thanks,

Steve

Jeebs · Jun 28, 2007

Click click.

Google is your best friend.

unsunghippie · Jun 28, 2007

Try This.

PrivateSub Form_Load()

If (App.PrevInstance = True) Then

MsgBox "Application already running"

Call someProcedure
EndIf

Mark Buskell · Jun 28, 2007

You need to get the handle (hwnd) of the the window. This gives you the name of the app. This is what you see now in the very top left of your screen. You then do a for-next-loop and compare any new application starting against existing windows opened and automatically close the app if it matches something already running.
You start this through a splash screen first and then load the main window.
There are examples on the VB sites showing how this is done.

Has your programmmer ever heard of a google search?

http://www.developerfusion.co.uk/show/134/

If the link this doesn't help him, PM me later on today and I will post some of my own code which by the way I got off the net.

aikona · Jun 28, 2007

unsunghippie said:
Try This.

PrivateSub Form_Load()

If (App.PrevInstance = True) Then

MsgBox "Application already running"

Call someProcedure
EndIf

Its not that simple ( to be foolproof)
you need to find the handle , define a mutex class and then use it in the main form (??!!) and you need to close your ( second) apps before any damage is done.

look at : http://faq.vb.free.fr/index.php?question=46 ( I know its in french , so what ,the code is in 'VB')

or at : http://www.xtremevbtalk.com/showthread.php?t=129256

if you type 'mutex VB6 application running' in google you'll have enough examples

Eric

unsunghippie · Jun 28, 2007

This has migrated off the PLC topic, but I don't understand why this would not be foolproof. If this code is placed as the first code in the startup form, and if someProcedure exits the app, the app should detect itself already running, and do nothing but display a message box, call the someProcedure and close. No harm, no foul. Remember, this is VB6 not .NET.

If I am missing something here, I am eager to learn.

panic mode · Jun 28, 2007

how about this (it's someone else's, not sure where I got it...)

aikona · Jun 28, 2007

unsunghippie said:
This has migrated off the PLC topic, but I don't understand why this would not be foolproof. If this code is placed as the first code in the startup form, and if someProcedure exits the app, the app should detect itself already running, and do nothing but display a message box, call the someProcedure and close. No harm, no foul. Remember, this is VB6 not .NET.

If I am missing something here, I am eager to learn.

Well I wrote some apps in Delphi with a 'check for apps allready running' and it worked ... on the develoment PC but not ( allways) on the user PC's ... did thid did that etc but eventualy this mutex beast does the trick everytime ( well at leadt on Win2000 and XP) .Maybe there are sublte ( microsoft) diferences between coding in VB or Delphi but looking at the net , I think that there is no easy solution.

Greeting

Eric

Steve Meisel · Jun 28, 2007

Thanks folks.

aikona · Jun 29, 2007

aikona said:
Well I wrote some apps in Delphi with a 'check for apps allready running' and it worked ... on the develoment PC but not ( allways) on the user PC's ... did thid(this) did that etc but eventualy this mutex beast does the trick everytime ( well at leadt(Least) on Win2000 and XP) .Maybe there are sublte(got a problem with this one)( microsoft) differences between coding in VB or Delphi but looking at the net , I think that there is no easy solution.

Greeting

Eric

Oops - sorry for all the spelling errors - no wonder my code never works

FrancisL · Jun 29, 2007

What exactly is wrong with using App.PrevInstance ?

aikona · Jun 29, 2007

FrancisL said:
What exactly is wrong with using App.PrevInstance ?

I don't know why it doesn't allways work .But have a look at the following links

http://vb.mvps.org/hardcore/html/handlingmultipleinstances.htm ...I think this link will answer your question better than I can

http://www.codeguru.com/forum/showthread.php?s=&threadid=293730

http://www.vbaccelerator.com/codelib/ssubtmr/startup.htm ( look at point 2)

Greetings Eric

FrancisL · Jun 29, 2007

I had a look.
It only does not work if you are running a copy of the exe file in another folder, or a copy with a different name in the same folder.
Given that is hardly seems worth the trouble of the API methods.
Francis

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