App.previnstance and command$

When my program opens,

if command$ = "" and app.previnstance then

now, this is the tricky part.
I want to activate my program which is already opened
and pass the value of the command$ line.

Condition: I can not use the forms caption to activate
it as it always displays a filename.

I have VB6.
Who is Participating?
clifABBConnect With a Mentor Commented:
Ok, here's how I would do it.

In your app, every time the caption changes, write that caption to the registry using SaveSetting().

When your all starts, check for previous instance and, if true, retrieve the caption from the registry and activate the app that way.

Also, pass the command string using the same method.  When your app is started, and there is a previous instance, write command$ to the registry.  In your app's main form's activate event, check for previous instance.  If false, retrieve command$ from the registry and use it.  Also, erease it immediately after retrieving it.

The code would look something like this:
Private Sub WriteCaption(sFilename As String)
  'This doesn't have to be a sub, but the save setting line
  'must go right after setting the form caption
  frmMain.Caption = sFilename
  SaveSetting "MyApp", "Activate", "Caption", sfilename
End Sub

Sub Main()
  Dim sCaption As String

  If App.PrevInstance Then
    SaveSetting "MyApp", "Activate", "Command", Command$
    sCaption = GetSetting("MyApp", "Activate", "Caption", "")
    AppActivate sCaption
  End If
End Sub

Private Sub Form_Activate ()
  Dim sCommand As String
  sCommand = GetSetting("MyApp", "Activate", "Command", "")
  If sCommand <> "" Then
    'Process Command
  End If
  DeleteSetting "MyApp", "Activate", "Command"
End Sub
put a title "mytitle" to your app and then modify app.title when it displays a filename to app.title=app.title & " " & filename.
Your second instance will have app.title and your previnstance app.title +filename.
Check app.previnstance at first line of code:
if app.previnstance then
dim firstapptitle as string

Search with findwindow(myclassname,firstapptitle)
dim hwnd as long
search again:
hwnd=(classname,firstapptitle + "*.*")
the hwnd to previous instance handle, set focus
with setfocus(hwnd)
to and exit
Oops, the activate event should test for previous instance.
Chang the code to this:

Private Sub Form_Activate ()
  Dim sCommand As String
  If Not App.PrevInstance Then
    sCommand = GetSetting("MyApp", "Activate", "Command", "")
    If sCommand <> "" Then
      'Process Command
    End If
    DeleteSetting "MyApp", "Activate", "Command"
  End If
End Sub
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