Question

I am attempted to write a small asynchronous socket library that I can use to create a client/server application. I can get all of the code to run fine if I leave it in the form, however if I try to move it out into its own class, I cannot figure out how to update the form with connection status, things like that. Below is code, shortened a bit just to make this easier to read and type.

Form Code:

Class Form1
Dim Network as NetworkModule

Public Sub Button1_Click(Sender, e) Handles Button1.Click
    Network = New NetworkModule("127.0.0.1", 1234)
End Sub
End Class 'Form1

NetworkModule class:

Class NetworkModule
    Private mSocket as Socket

    Public Sub New(IP as string, Port as Integer)
        Dim remoteEP as New IPEndpoint(IP.Parse(IP), Port)
        mSocket = New Socket(internetwork, stream, tcp)
        mSocket.BeginConnect(remoteEP, New AsyncCallback(AddressOf onConnect), mSocket)
        Notify("Connection to " & remoteEP.ToString)  'This one works
     End Sub 'New

     Private Sub onConnect(ar as IAsyncResult)
         mSocket = CType(ar.AsyncState, Socket)
         mSocket.EndConnect(ar)
         Notify("Connected")  'This one never shows
     End Sub 'onConnect

    Private Delegate Sub _Notify(Msg as String)
    Private Sub Notify(Msg as String)
        If Form1.txtLog.InvokeRequired Then
            Form1.txtLog.Invoke(New _Notify(AddressOf Notify), Msg)
            Exit Sub
        End if
        Form1.txtLog.Text &= Msg & vbcrlf
    End Sub 'Notify
End Class 'NetworkModule

There is actually more to that class, but I never get anything after the first message goes out. I’m not sure where to go from here. I’ve tried lots of different methods that I’ve found on the google searches, some from here, some not. Anybody have any ideas?

Answer 1

Here’s how I would rewrite it:

Class Form1
    Private Network as NetworkModule
    Public NotifyDelegate As NetworkModule.NotifyDelegate

    Public Sub New()
        NotifyDelegate = New NetworkModule.NotifyDelegate(AddressOf Notify)
    End Sub

    Public Sub Button1_Click(Sender, e) Handles Button1.Click
        Network = New NetworkModule("127.0.0.1", 1234, Me)
    End Sub

    Public Sub Notify(Msg As String)
        txtLog.Text &= Msg & vbCrLf
    End Sub
End Class 'Form1

NetworkModule Class (partial):

Class NetworkModule
    Public Delegate Sub NotifyDelegate(Msg as String)

    Private Sub Notify(Msg as String)
        If m_Form.InvokeRequired Then
            m_Form.Invoke(Form1.NotifyDelegate, Msg)
        Else
            m_Form.Notify(Msg)
        End If
    End Sub 'Notify

    Private mSocket as Socket

    Private m_Form As Form1

    Public Sub New(IP as string, Port as Integer, oForm As Form1)
        m_Form = oForm
        Dim remoteEP as New IPEndpoint(IP.Parse(IP), Port)
        mSocket = New Socket(internetwork, stream, tcp)
        mSocket.BeginConnect(remoteEP, New AsyncCallback(AddressOf onConnect), mSocket)
        Notify("Connection to " & remoteEP.ToString)  'This one works
     End Sub 'New

Update with Interface approach

A better mechanism than passing the form itself is to implement an interface. To do this, first create the interface definition (note that the delegate has moved to the Interface for convenience):

Public Interface INotify
    Sub Notify(Msg As String)
    Delegate Sub NotifyDelegate(Msg As String)
End Interface

Then Implement the interface in the Form. Note that the form now determines whether or not Invoke is required. This allows the INotify interface to be used in non-UI scenarios, such as logging to disk or the event log.

Public Class Form1
    Implements INotify

    Public Sub Notify(Msg As String)
        txtLog.Text &= Msg & vbCrLf
    End Sub

    Private Sub INotify_Notify(Msg As String) Implements INotify.Notify
        If Me.InvokeRequired Then
            Me.Invoke(New INotify.NotifyDelegate(AddressOf Notify), Msg)
        Else
            Me.Notify(Msg)
        End If
    End Sub 'Notify

    Private Network As NetworkModule

    Public Sub Button1_Click(Sender, e) Handles Button1.Click
        Network = New NetworkModule("127.0.0.1", 1234, Me)
    End Sub
End Class 'Form1

Finally, store a reference to the INotify interface instead of the Form in NetworkModule (note the NetworkModule no longer needs to know or care that an Invoke may be required):

Public Class NetworkModule
    Public Delegate Sub NotifyDelegate(Msg As String)

    Private m_Notifier As INotify

    Private Sub Notify(Msg As String)
        m_Notifier.Notify(Msg)
    End Sub 'Notify

    Public Sub New(IP As String, Port As Integer, oNotifier As INotify)
        m_Notifier = oNotifier
        ' The addition code here
    End Sub 'New
End Class