Disallowing multiple instances of a VB App 2

Try this in your app initialisation code<br>
<br>
If App.Previnstance then<br>
&nbsp;&nbsp;&nbsp;&nbsp;Unload Me ' or whatever will make your app go away<br>
&nbsp;&nbsp;&nbsp;&nbsp;Exit Sub<br>
End If<br>
<p>Mike Lacey<br><a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a><br><a href= Cargill's Corporate Web Site</a><br>

<br>
Thanks Mike , this works<br>
<br>
The problem is that it is too simple (-:<br>
<br>
Tarek

Hey Mike,<br>
I like that one it sure is small.<br>
<br>

I just found this other solution that is a tad more involved but will allow you to actually switch over to the running instance (Win95 and NT4 only -- will not work for Win98):<br>
<br>
Public Declare Function FindWindow Lib &quot;user32&quot; Alias &quot;FindWindowA&quot; (ByVal lpClassName As String, ByVal lpWindowName As String) As Long<br>
<br>
Public Declare Function SetForegroundWindow Lib &quot;user32&quot; Alias &quot;SetForegroundWindow&quot; (ByVal hwnd As Long) As Long<br>
<br>
Private Sub Form_Load()<br>
<br>
Dim hdl As Long<br>
Dim rc As Long<br>
<br>
hdl = FindWindow(vbNullString, &quot;The Real Caption&quot<br>
If hdl &gt; 0 Then<br>
rc = SetForegroundWindow(hdl)<br>
End<br>
Else<br>
Me.Caption = &quot;The Real Caption&quot;<br>
End If<br>
<br>
End Sub<br>
<br>
Here's how it works (there's a trick described later):<br>
<br>
The FindWindow API requires exact description of the Window you're trying to find. The API returns a handle to the Instance that's running. If the handle is 0 then there is no other instance; otherwise, we feed the handle to the SetForegroundWindow API to make that instance the front app.<br>
<br>
The trick is this: as mentioned in the original post, as soon as the application starts, the FindWindow will a return a reference to itself (the new instance). This means that we would really never know whether or not there is another instance. So here's what we do:<br>
<br>
At design time, change the caption of the main form to some &quot;dummy&quot; text. When the application starts, use the &quot;real&quot; caption as the parameter in the FindWindow API. If the API returns non-zero then switch to the app; otherwise, change the caption of the form to the &quot;real&quot; text and continue on with the app.<br>
<br>
It seems complicated but it is real simple and works well (on Win/95 and Win/NT only). Win98 and Win2000 do not allow you to change the focus to another application -- or something like that (do not quote me on this one)<br>
<br>
Remember, if you don't need to switch over to the running instance then use Mike's code above -- it's simple and very effective.<br>
<br>
Tarek

Thanks Tarek - interesting. I'm looking forward to seeing Dan Appleman's new book (I'm presuming that there will be one) about the Win2000 API - should be fun.<br>
-ml<br>
<p>Mike Lacey<br><a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a><br><a href= Cargill's Corporate Web Site</a><br>

I have tried the app.previnstance in order to end the project if there is one already open, but the problem is that the app.previnstanve always = false no matter how many instances of the project i have open. I use the app.previnstance command in the mainmodule sub main. does anybody have any ideas???

Really? What operating system and version of VB are you using?<br>
<br>
Mike<br>
<p>Mike Lacey<br><a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a><br><a href= Cargill's Corporate Web Site</a><br>

Mike I am using vb5 and win 98. No matter how many times the application is open the App.PrevInstance always = false. This happens when I am running in debug mode and also when I build an exe with the code in it it still allows me to open multiple instances. I cannot figure out why. Do you have any other ideas how I can stop multiple instances???? All ideas welcome????

Sorry, guys, I find this thread almost laughable since my goal is to do the opposite: keep two instances of an app running, no matter what happens.<br>
The answer will be here.<br>
Not a question. But any post could be the solution to my problem..<br>

Gettoblaster - have you tried vb400's findwindow code? <p>Mike Lacey<br><a href=mailto:Mike_Lacey@Cargill.Com>Mike_Lacey@Cargill.Com</a><br><a href= Cargill's Corporate Web Site</a><br>