[RESOLVED] Delegate Problem

Creating a simple program to monitor changes to Network Adapter(s) status, vis:

Code:

---

Imports System
Imports System.Net
Imports System.Net.NetworkInformation
Public Class Form1

    Private Delegate Sub DoResults(ByVal nName As String, ByVal nStatus As String)

    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        AddHandler NetworkChange.NetworkAddressChanged, AddressOf AddressChangedCallback
        TextBox1.Text = "Monitoring for changes"
        TextBox1.AppendText(vbNewLine)
    End Sub

    Private Sub UpdateText(ByVal AdapterName As String, ByVal AdapterStatus As String)
        TextBox1.AppendText(AdapterName)
        TextBox1.AppendText(" ")
        TextBox1.AppendText(AdapterStatus)
        TextBox1.AppendText(vbNewLine)
    End Sub

    Private Sub AddressChangedCallback(ByVal sender As Object, ByVal e As EventArgs)
        Dim adapters As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
        Dim n As NetworkInterface
        For Each n In adapters
            Dim adResult As New DoResults(AddressOf UpdateText)
            Try
                adResult.Invoke(n.Name.ToString, n.OperationalStatus.ToString)
            Catch ex As Exception
                MessageBox.Show("Exception: " & ex.Message)
            End Try
        Next n
    End Sub
End Class

---

I'm getting an "Cross-thread operation not valid: Control Textbox1 accessed from a thread other than the thread it was created on" exception when I invoke the Delegate. Clearly there's a gap in my understanding; can someone perhaps explain what I ought to be doing ?

I appear to have resolved this

Code:

---

    Private Sub AddressChangedCallback(ByVal sender As Object, ByVal e As EventArgs)
        Dim adapters As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
        Dim n As NetworkInterface
        For Each n In adapters
            Dim adResult As New DoResults(AddressOf UpdateText)
            Try
                Me.Invoke(adResult, n.Name.ToString, n.OperationalStatus.ToString)
            Catch ex As Exception
                MessageBox.Show("Exception: " & ex.Message)
            End Try
        Next n
    End Sub

---

whether it's the 'best' way or not I don't know

No need to write custom delegates. Use the Action(Of T delegate or the MethodInvoker delegate. Side note Use Environment.NewLine over VbNewline. It's a is a string containing \r\n which are escape characters for return and new line vbNewLine is char 10 and char 13. The runtime decides which one to used based on the platform its being run on.

vb Code:

Imports System
Imports System.Net
Imports System.Net.NetworkInformation
 
Public Class Form1
 
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        AddHandler NetworkChange.NetworkAddressChanged, AddressOf AddressChangedCallback
        Me.TextBox1.Text = "Monitoring for changes"
        Me.TextBox1.AppendText(Environment.NewLine)
    End Sub
 
    Private Sub UpdateText(ByVal AdapterName As String, ByVal AdapterStatus As String)
        Me.TextBox1.AppendText(String.Format("{0} {1}{2}",
                                             AdapterName,
                                             AdapterStatus,
                                             Environment.NewLine))
    End Sub
 
    Private Sub AddressChangedCallback(ByVal sender As Object, ByVal e As EventArgs)
        Dim adapters As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
        Dim n As NetworkInterface
        For Each n In adapters
            Try
                Me.Invoke(New MethodInvoker(Sub() UpdateText(Name.ToString, n.OperationalStatus.ToString)))
            Catch ex As Exception
                MessageBox.Show("Exception: " & ex.Message)
            End Try
        Next n
    End Sub
End Class

You could get rid of UpdateStatus altogether:-

vbnet Code:

'
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        AddHandler NetworkChange.NetworkAddressChanged, AddressOf AddressChangedCallback
 
        TextBox1.Text = "Monitoring for changes"
        TextBox1.AppendText(Environment.NewLine)
    End Sub
 
    Private Sub AddressChangedCallback(sender As Object, e As EventArgs)
 
        Dim adapters As NetworkInterface() = NetworkInterface.GetAllNetworkInterfaces()
        Dim n As NetworkInterface
        For Each n In adapters
 
            Try
                TextBox1.Invoke(Sub()
                                    TextBox1.AppendText(n.Name & " " & n.OperationalStatus.ToString & Environment.NewLine)
                                End Sub)
 
            Catch ex As Exception
                MessageBox.Show("Exception: " & ex.Message)
            End Try
        Next n
    End Sub

You could even get rid of the AddressChangedCallback sub too if you wanted to get really terse.