[RESOLVED] Threading / Delegates

[Doogle]

I'm getting myself really confused.

The idea is to Ping all the addresses in a given Class C sub-net and analyse the responses. Doing this synchronously takes a long time so I thought I'd use the Threading capability of VB2008 to start a new thread to Ping each Address, using Delegates to start the thread and process the results.

Public Class Form1
    Private Delegate Sub DoResult(ByVal pr As PingReply)
    Private Delegate Sub StartPing(ByVal IPCNumber As Integer)
    Private IPSubNet As String

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        IPSubNet = "192.168.1"
        For IPCounter As Integer = 0 To 254
            Dim myPing As StartPing = AddressOf DoPing
            Dim PingParam As Integer = IPCounter
            myPing.Invoke(PingParam)
        Next
    End Sub

    Public Sub ShowResult(ByVal pr As PingReply)
        Debug.Print("Address: " + pr.Address.ToString + " Status: " + pr.Status.ToString)
    End Sub

    Public Sub DoPing(ByVal ipn As Integer)
        Dim IPToPingC As String = IPSubNet + ipn.ToString
        Dim PingOp As New Ping
        Dim Pingresult As PingReply = PingOp.Send(IPToPingC)
        Dim ADResult As New DoResult(AddressOf ShowResult)
        ADResult.Invoke(Pingresult)
    End Sub
End Class

The above is failing with a Null Exception at ' Debug.Print("Address: " + pr.Address.ToString + " Status: " + pr.Status.ToString)'
Having used the Debugger to look at PingResult in DoPing it's Null, I don't understand why? At the point of failure, IPToPingC has a vaule of "192.168.1.10" and nothing is being output to the Debug Window (so what happened to "192.168.1.0" through to "192.168.1.9" is anyones guess) - and I've only just started using VB2008.

Never having used Threading I think I'm a little (lot) out of my depth, any assistance would be gratefully received.

EDIT: Now realised that I should perhaps be using DynamicInvoke for starting DoPing and using Object type as the parameter rather than Invoke but it then fails with :
A first chance exception of type 'System.MissingMemberException' occurred in Microsoft.VisualBasic.dll
A first chance exception of type 'System.Reflection.TargetInvocationException' occurred in mscorlib.dll

EDIT2: Just realised what the error message means - I have left the final period off the IPSubNet assignment. It now doesn't fail, but I'm getting wierd results

Address: 192.168.1.104 Status: DestinationHostUnreachable
Address: 192.168.1.1 Status: Success
Address: 192.168.1.104 Status: DestinationHostUnreachable
Address: 192.168.1.104 Status: DestinationHostUnreachable
Address: 192.168.1.104 Status: DestinationHostUnreachable
Address: 192.168.1.104 Status: DestinationHostUnreachable

192.168.1.1 is the gateway and 192.168.1.104 is the address of the PC running this code. Obviously there's some sort of re-synchronisation problem or the code is just not doing what I think it should.
Current stae of the code:

Imports System.Net.NetworkInformation
Imports System.Threading

Public Class Form1
    Private Delegate Sub DoResult(ByVal pr As PingReply)
    Private Delegate Sub StartPing(ByVal IPAdd As Integer)
    Private IPSubNet As String

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        IPSubNet = "192.168.1."
        For IPCounter As Integer = 0 To 254
            Dim myPing As StartPing = AddressOf DoPing
            Dim PingParam As Integer = IPCounter
            myPing.DynamicInvoke(PingParam)
        Next
    End Sub

    Public Sub ShowResult(ByVal pr As PingReply)
        Debug.Print("Address: " + pr.Address.ToString + " Status: " + pr.Status.ToString)
    End Sub

    Public Sub DoPing(ByVal ipn As Integer)
        Dim IPToPingC As String = IPSubNet + ipn.ToString
        Dim PingOp As New Ping
        Dim Pingresult As PingReply = PingOp.Send(IPToPingC)
        Dim ADResult As New DoResult(AddressOf ShowResult)
        ADResult.Invoke(Pingresult)
    End Sub
End Class