Multi Threading For getting links from Webbrowser1.Document - vb.net

Question

The problem is that multi threading is not working properly for getting links from webbrowser1.document.links. How can I solve this problem?
Public Class Form1
Dim thread1 As System.Threading.Thread
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
thread1 = New System.Threading.Thread(AddressOf GetLinks)
thread1.Start()
End Sub
Private Sub GetLinks()
For i As Integer = 0 To WebBrowser1.Document.Links.Count - 1
If TextBox1.Text.Length > 0 Then
TextBox1.Text += Environment.NewLine & WebBrowser1.Document.Links(i).ToString
Else
TextBox1.Text = WebBrowser1.Document.Links(i).ToString
End If
Next
End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
WebBrowser1.Navigate("www.google.com")
Me.CheckForIllegalCrossThreadCalls = False
End Sub
End Class

Answer 1

You can't make a call to one of the controls on the form (in this case, TextBox1 and WebBrowser1) from another thread other than the main thread of the form. You need to use a delegate.
This will do the trick:
Private _iLinks As Integer
Dim thread1 As System.Threading.Thread
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
CheckForIllegalCrossThreadCalls = False
_iLinks = WebBrowser1.Document.Links.Count
thread1 = New System.Threading.Thread(AddressOf GetLinks)
thread1.Start()
End Sub
Private Sub GetLinks()
For i As Integer = 0 To _iLinks - 1
UpdateTextBoxDelegate(i)
Next
End Sub
Private Sub UpdateTextBox(ByVal iLink As Integer)
If TextBox1.Text.Length > 0 Then
TextBox1.Text += Environment.NewLine & WebBrowser1.Document.Links(iLink).ToString
Else
TextBox1.Text += WebBrowser1.Document.Links(iLink).InnerText.ToString()
End If
End Sub
Private Delegate Sub UpdateTextBoxCallback(ByVal iLink As Integer)
Private Sub UpdateTextBoxDelegate(ByVal iLink As Integer)
Try
If Me.InvokeRequired Then
Dim cb As New UpdateTextBoxCallback(AddressOf UpdateTextBox)
Me.Invoke(cb, New Object() {iLink})
Else
UpdateTextBox(iLink)
End If
Catch ex As Exception
MessageBox.Show("There was an error " + ex.Message, "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
End Try
End Sub
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
WebBrowser1.Navigate("http://stackoverflow.com/")
End Sub