VB Forum / General / July 2009

If by "opened" you mean loaded and visible, then something like this may
do the job.

If FormIsLoaded(Form1.Name) And Form1.Visible Then
    'do whatever
End If

Public Function FormIsLoaded(ByVal sFormName As String) As Boolean
    Dim bLoaded As Boolean
    Dim f As Form

    bLoaded = False

    For Each f In Forms
        If f.Name = sFormName Then
            bLoaded = True
            Exit For
        End If
    Next f

    Set f = Nothing

    FormIsLoaded = bLoaded
End Function

I'll leave to you the problem of how your client app is going to talk to
your remote app which will have to run the above code and return the answer.

You could do something simple like open a file (exclusive)when you load the
form and close it when you exit the form. Then all the client form needs to
do is to check to see if it can write to the file. If you get an error then
the form is open...

It probaly the simliest method. Of course if your app terminates abruptly
you might leave the file open and will need to forcibly close it on the next
run.

I would use Winsock for this. The main or server app listens to incoming
connections, and the clients connect to it using TCP. Below is a sample
code. To try it, add 1 command button with name "btnSend", and 2 Winsock
controls to Form1. Set the name for the first one to "wsckServer", and Index
property to 0, and "wsckClient" for the second one while leave Index
property blank, then add the following code:

Option Explicit

Private Sub Form_Load()
   ' Server
   wsckServer(0).LocalPort = 5555
   wsckServer(0).Listen

   ' Client
   wsckClient.RemotePort = 5555
   wsckClient.RemoteHost = "127.0.0.1" ' Local host
End Sub

' Server side =======================================

Private Sub wsckServer_ConnectionRequest(Index As Integer, _
   ByVal requestID As Long)
   wsckServer(GetNextAvailableSocket()).Accept requestID
End Sub

Private Sub wsckServer_DataArrival(Index As Integer, ByVal bytesTotal As
Long)
   Dim s As String

   wsckServer(Index).GetData s, vbString
   Debug.Print "wsckServer_DataArrival: s = '" & s & "'"

   Select Case Left(s, 3)
       Case "001":
           ' Send response
           wsckServer(Index).SendData "Ack"
   End Select
End Sub

' Get the next available socket, or load a new one if all are used
Private Function GetNextAvailableSocket() As Long
   Dim iNext As Long
   Dim iWinsockControlsCount As Long
   Dim ctl As Control

   iNext = 0 ' Assume no unused socket found
   For Each ctl In Me.Controls
       If TypeOf ctl Is Winsock Then
           If ctl.Name = "wsckServer" Then
               If ctl.Index > 0 Then ' Avoid the first socket
                   If ctl.State = sckClosed Then
                       ' Found unused socket
                       iNext = ctl.Index
                       Exit For
                   End If
                   ' Keep track of the maximum Index number
                   If iWinsockControlsCount < ctl.Index Then
                       iWinsockControlsCount = ctl.Index
                   End If
               End If
           End If
       End If
   Next

   If iNext = 0 Then
       iNext = iWinsockControlsCount + 1
       Load wsckServer(iNext)
   End If

   Debug.Print "GetNextAvailableSocket: returning " & iNext
   GetNextAvailableSocket = iNext
End Function

' Client side  =======================================

Private Sub btnSend_Click()
   Dim t As Single

   wsckClient.LocalPort = 0 ' Use dynamic port
   wsckClient.Connect

   ' Wait for up to 5 seconds to connect, or use the Connect event
   t = Timer
   Do While Timer - t < 5 And wsckClient.State <> sckConnected
       DoEvents
   Loop

   If wsckClient.State = sckConnected Then
       wsckClient.SendData "001"
   Else
       Debug.Print "Timeout waiting to connect"
   End If
End Sub

Private Sub wsckClient_DataArrival(ByVal bytesTotal As Long)
   Dim s As String

   wsckClient.GetData s, vbString
   Debug.Print "wsckClient_DataArrival: s = '" & s & "'"

   Select Case Left(s, 3)
       Case "Ack":
           ' Add code here
   End Select
End Sub