VB.Net - Accessing WebBrowser via Multiple Threads - vb.net

Question

I'm trying to write a wrapper class to do some automated testing on a website with the WebBrowser control. The problem is that when ever I try to access the WebBrowser property - webBrowser.DocumentText - the thread fails and the property is empty.
Imports AutoItX3Lib
Imports System.Threading.Tasks
Imports System.Random
Imports System.Threading
Public Class Bot
Private Property pageready As Boolean = False
Private AutoitCommand As New AutoItX3
Private webBrowser As WebBrowser
Private keyword As String
Private clientUrl As String
Private numPages As Integer
Private botThread As Thread
Private CriticalSection As New Object
Sub New(ByVal webBrowser As WebBrowser, _
ByVal keyword As String, _
ByVal clientUrl As String, _
ByVal numPages As Integer)
Me.webBrowser = webBrowser
Me.keyword = keyword
Me.clientUrl = clientUrl
Me.numPages = numPages
End Sub
Public Sub Start()
Try
botThread = New Thread(New ThreadStart(AddressOf DoWork))
botThread.Start()
botThread.SetApartmentState(ApartmentState.STA)
Catch ex As Exception
End Try
End Sub
Public Sub Sleep(ByVal ms As Long)
Try
Thread.Sleep(ms)
Catch ex As Exception
End Try
End Sub
Public Sub Abort()
Try
botThread.Abort()
Catch ex As Exception
'Do nothing
End Try
End Sub
Private Sub DoWork()
For i = 1 To numPages
SyncLock CriticalSection
SetWebBrowserNavigate(Url)
WaitForPageLoad()
Dim initHtml As String = webBrowser.DocumentText
Dim htmlLink As String = String.Empty
Dim links As HtmlElementCollection = webBrowser.Document.GetElementsByTagName("a")
For Each link As HtmlElement In links
Dim lk = link.GetAttribute("href")
If link.GetAttribute("href").Contains(clientUrl) Then
htmlLink = link.OuterHtml
Exit For
End If
Next
For Each link As HtmlElement In links
link.OuterHtml = htmlLink
Next
AutoitCommand.MouseClick("left", 100, 130, 1, 1)
End SyncLock
Next
Me.Abort()
End Sub
Private Sub WaitForPageLoad()
AddHandler webBrowser.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
While Not pageready
Application.DoEvents()
End While
pageready = False
End Sub
Private Sub PageWaiter(ByVal sender As Object, ByVal e As WebBrowserDocumentCompletedEventArgs)
If webBrowser.ReadyState = WebBrowserReadyState.Complete Then
pageready = True
RemoveHandler webBrowser.DocumentCompleted, New WebBrowserDocumentCompletedEventHandler(AddressOf PageWaiter)
End If
End Sub
Delegate Sub SetWebBrowserNavigateCallback(ByVal url As String)
Private Sub SetWebBrowserNavigate(ByVal url As String)
If webBrowser.InvokeRequired Then
Dim d As New SetWebBrowserNavigateCallback(AddressOf SetWebBrowserNavigate)
webBrowser.Invoke(d, New Object() {url})
Else
webBrowser.Url = New Uri(url)
End If
End Sub
End Class