VB.net Simple Multithreading help..

Question

I have a Private Sub Fill(), which im trying to call from button1, in the form of

Dim t1 As System.Threading.Thread = New System.Threading.Thread(AddressOf Me.Fill)

t1.Start()

However, when I run the program nothing happens. I click the button numerous times and the function isnt being executed. What gives? The Fill function is basically a outputting bunch of html from IE into a textbox, running regex and outputting the results in a listbox.

Can anyone help me get this working? I'd appreciate the help. EDIT: Below, is the Fill function that I am trying to get working. The function itself works, when i try it without multithreading. But not with it...

Private Sub Fill()
    Try
        For Each links In ListBox2.Items
            Dim blah As Boolean = False

            Do While blah = False


                Application.DoEvents()









                If WebBrowser1.ReadyState = WebBrowserReadyState.Complete Then


                    blah = True
                    WebBrowser1.Navigate(links)
                    Application.DoEvents()
                    Me.Refresh()

                    'OUTPUT THE REGEX IN RTB
                    Try

                        RichTextBox1.Text = WebBrowser1.Document.Body.OuterHtml
                        RichTextBox1.Update()

                        Application.DoEvents()
                        Me.Refresh()
                        'INTRODUCE REGEX
                        If CheckBox1.Checked = True Then
                            Dim R As New Regex("</H3>&lt;.*gt;")

                            For Each M As Match In R.Matches(RichTextBox1.Text)


                                Dim email As String = M.Value.Substring(9).Split("&;").GetValue(0).ToString

                                ListBox1.Items.Add(email)
                            Next
                        End If
                    Catch ex As Exception
                        Label1.Text = "Error recieved. Program will not stop"
                        Me.Refresh()

                    End Try

                    Application.DoEvents()
                    Me.Refresh()

                End If
            Loop



        Next
    Catch ex As Exception

    End Try





End Sub

Answer 1

Start by placing a breakpoint inside the Fill method. I bet it starts up just fine.

Answer 2

I think you are having problems because you are not on the UI thread when you are trying to write to the textbox in the Fill() method – this will causes an exception. To solve the problem you need to switch to the UI thread using BeginInvoke and a delegate as in the example below:

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim t1 As System.Threading.Thread = New System.Threading.Thread(AddressOf Me.Fill)
        t1.Start()

End Sub

Private Delegate Sub FillDelegate()

Private Sub Fill()
        If TextBox1.InvokeRequired Then
            TextBox1.BeginInvoke(New FillDelegate(AddressOf Fill))
        Else
            TextBox1.Text = "Worked!!!!"
        End If
End Sub