Use running instance to execute commandline in vb.net

Question

I'd like to use a running instance of my application (a single instance application) to run a new commandline... I've heard about mutexes and IPC mechanisms but I don't know how to use it.

Explanation :

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        MsgBox(Environment.CommandLine)
    End Sub

End Class

Example :

I launch the app with a file as argument, it shows the MsgBox and I let it run. If I launch once again the app with a file as argument, it won't show the MsgBox... How can I show it with the new commandline ?

Regards, Drarig29.

Answer 1

In VB.NET you can make your application single instance from the project properties page. Check the "Make single instance application" option, then click the "View Application Events" button:

In the ApplicationEvents.vb class, add a handler for StartupNextInstance - this will be called when the application is already running and you start it again. You can call a method on your main form:

Namespace My

    Partial Friend Class MyApplication

        Private Sub MyApplication_StartupNextInstance(sender As Object, e As ApplicationServices.StartupNextInstanceEventArgs) Handles Me.StartupNextInstance
            ' Handle arguments when app is already running
            If e.CommandLine.Count > 0 Then
                ' Pass the argument to the main form
                Dim form = TryCast(My.Application.MainForm, Form1)
                form.LoadFile(e.CommandLine(0))
            End If
        End Sub

    End Class

End Namespace

In your main form, you can pass the initial command line arguments, and handle the subsequent ones, with a common method:

Public Class Form1

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
        ' Handle arguments from the initial launch
        Dim args = Environment.GetCommandLineArgs()
        If args.Length > 1 Then
            LoadFile(args(1))
        End If
    End Sub

    Public Sub LoadFile(filename As String)
        MessageBox.Show(filename)
    End Sub

End Class