Communication between vb.net applications

Question

Hey all i found this code here in C# that allows the use of SendMessage API to send messages back and forth from 2 .net applications running. Everything goes well in the C# code when testing but i needed to convert it to VB.net.

So i used an online C#->VB.net converter and got this:

Imports System.Runtime.InteropServices

Public Class Form1
    Inherits System.Windows.Forms.Form
    Private Const RF_TESTMESSAGE As Integer = &HA123

    <DllImport("user32.dll", CharSet:=CharSet.Auto, SetLastError:=True)> _
    Public Shared Function SendMessage(ByVal hwnd As IntPtr, <MarshalAs(UnmanagedType.U4)> ByVal Msg As Integer, ByVal wParam As IntPtr, ByVal lParam As IntPtr) As Integer
    End Function

    Public Sub New()
        InitializeComponent()
        Me.Text = String.Format("This process ID: {0}", Process.GetCurrentProcess().Id)
    End Sub

    <STAThread()> Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        Application.EnableVisualStyles()
        Application.Run(New Form1())
    End Sub

    Private Sub button1_Click(ByVal sender As Object, ByVal e As System.EventArgs)
        Dim proc As Process = Process.GetCurrentProcess()
        Dim processes As Process() = Process.GetProcessesByName(proc.ProcessName)

        If processes.Length > 1 Then
            For Each p As Process In processes
                If p.Id <> proc.Id Then
                    SendMessage(p.MainWindowHandle, RF_TESTMESSAGE, IntPtr.Zero, IntPtr.Zero)
                End If
            Next
        Else
            MessageBox.Show("No other running applications found.")
        End If
    End Sub

    Protected Overrides Sub WndProc(ByRef message As Message)
        If message.Msg = RF_TESTMESSAGE Then
            ListBox1.Items.Add("Received message RF_TESTMESSAGE")
        End If

        MyBase.WndProc(message)
    End Sub
End Class

However, using the code above for both my apps doesnt seem to produce any sendmessage action when it gets to the If processes.Length > 1 Then. It always tells me No other running applications found. even though i have both apps running as i did in the C# example.

I must be missing something that didnt carry over when converting. Any help would be great to fix this!

Answer 1

The fact that you are getting the "No other running applications found" message indicates a problem in this bit of code. Check out my notes here:

    Dim proc As Process = Process.GetCurrentProcess()
    //This gets an array of all processes currently running with the same name
    //  as this application.  
    Dim processes As Process() = Process.GetProcessesByName(proc.ProcessName)

    //If there is only one process with this application's name, then it's
    //  THIS process, so there aren't any others by the same name running
    //  right now.  
    If processes.Length > 1 Then
        For Each p As Process In processes
            If p.Id <> proc.Id Then
                SendMessage(p.MainWindowHandle, RF_TESTMESSAGE, IntPtr.Zero, IntPtr.Zero)
            End If
        Next
    Else
        //Thus, this gets called because there are not other applications with 
        //the same name.
        MessageBox.Show("No other running applications found.")
    End If

Please be aware that when you run code in the environement, modern studio version usually show up as DevEnv.exe, so running two instances of the IDE should normally work. However! There is an option in Visual Studio to run the code under its own application (executable) name. If you go to your Project Properties --> Debug, there is an option labeled Enable the Visual Studio hosting process. Disabling that checkbox will cause the code to run under the name of its compiled executable.