Multithreading duplicate error after background worker added - vb.net

Question

I wrote a program that does queries on some search engines that I wanted to be multithreaded so it could do the searches faster. I made a question about this which was answered indirectly, but I have yet another problem even after I set up delegates and such.
I was running the queries on the main thread, so I had to set up a BackgroundWorker. I did that but even though everything seems to run without an issue, I get duplicates of my results even though the program is suppose to do the opposite. Sometimes it doesn't even read or output a result that I know would be good.
Imports System.Net
Imports System.IO
Imports System.ComponentModel
Public Class Form2
Dim i As Integer
Dim SearchString As String
Public CleanSearchStrings As String()
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
i = RichTextBox1.Lines.Count
BackgroundWorker1.RunWorkerAsync()
End Sub
Private Sub StartThreads()
While i > 0
i = i - 1
Dim thread_count As String = Process.GetCurrentProcess().Threads.Count - 20
Label_T(thread_count)
SearchString = LineFunc(i)
Threading.Thread.Sleep(500)
SearchString = Ask_Query(SearchString) #This was commented out
SearchString = Bing_Query(SearchString) #just simple webscraping
SearchString = Yahoo_Query(SearchString)
If SearchString.Contains("All_Query:Yes") Then
SearchString = SearchString.Replace("All_Query:Yes", "")
RTB(SearchString)
End If
End While
End Sub
Private Delegate Sub UpdateStatus(ByVal s As String)
Private Delegate Sub UpdateLabel(ByVal thread_count As String)
Private Delegate Function Line(ByVal i As Integer)
Function LineFunc(ByVal i As Integer)
If Me.InvokeRequired Then
Me.Invoke(New Line(AddressOf LineFunc), New Object() {i})
Else
SearchString = RichTextBox1.Lines(i).ToString
Return SearchString
End If
End Function
Sub RTB(ByVal s As String)
If Me.InvokeRequired Then
Me.Invoke(New UpdateStatus(AddressOf RTB), New Object() {s})
Else
RichTextBox2.AppendText(Environment.NewLine & s)
End If
End Sub
Sub Label_T(ByVal thread_count As String)
If Me.InvokeRequired Then
Me.Invoke(New UpdateLabel(AddressOf Label_T), New Object() {thread_count})
Else
Label3.Text = "Threads Running: " + thread_count
End If
End Sub
Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork
BackgroundWorker1.WorkerSupportsCancellation = True
BackgroundWorker1.WorkerReportsProgress = True
Dim count As Integer
Dim num As Integer = TextBox1.Text - 1
For count = 0 To num
Dim thread = New Threading.Thread(AddressOf StartThreads)
thread.IsBackground = True
thread.Start()
Threading.Thread.Sleep(500)
Next
End Sub
End Class
I know it has something to do with the LineFunc that I wrote but I can't seem to figure it out.
This was working flawlessly on multithreading, but the UI would be frozen and after I added the BackgroundWorker it seems to be giving me these duplicate results error and not reading the TextBox fully.
Update:
Private Sub StartThreads()
For count = count To i
Dim SearchString As String = LineFunc(count)
count += 1
Dim thread_count As String = CType(Process.GetCurrentProcess().Threads.Count - 20, String)
Label_T(thread_count)
Threading.Thread.Sleep(500)
SearchString = CType(Ask_Query(SearchString), String)
SearchString = CType(Bing_Query(SearchString), String)
SearchString = CType(Yahoo_Query(SearchString), String)
If SearchString.Contains("All_Query:Yes") Then
SearchString = SearchString.Replace("All_Query:Yes", "")
RTB(SearchString)
End If
Next
End Sub
Heres my Revised Get Line Func
Private Delegate Function GetTextBox(ByVal index As Integer) As String
Public Function LineFunc(ByVal index As Integer) As String
If Me.InvokeRequired Then
Me.Invoke(New GetTextBox(AddressOf LineFunc), New Object() {index})
Else
Dim indexSearchString As String
indexSearchString = CType(RichTextBox1.Lines(index), String)
Return indexSearchString
End If
End Function
If i use the a msgbox it gives me the right values i don't understand how come it does not give me the right values when i do the func Dim SearchString As String = LineFunc(count) it returns a null string in the end i don't understand why
this seemed to work for the duplicate issue but now i seem to be having issues with my output to richtextbox2 only outputing blanks and the line func is only giving out blanks i don't understand why either but atleast there is progress

Answer 1

I can't verify if this will work as you haven't posted the search functions, but here goes.
Public Class Form2
Dim i As Integer
Dim SearchString As String
Dim ResultString As String
Public CleanSearchStrings As String()
Private threadCount As Integer
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
SearchUsingRTB1Items()
End Sub
Private Sub SearchUsingRTB1Items()
threadCount = 0
Dim rtb1Lines() As String = RichTextBox1.Lines
Parallel.ForEach(rtb1Lines, Sub(line As String)
dim ResultString As String =""
threadCount += 1
Label_T(i.ToString)
ResultString =Ask_Query(line) 'This was commented out
ResultString = ResultString & Bing_Query(line) 'just simple webscraping
ResultString = ResultString & Yahoo_Query(line)
If ResultString.Contains("All_Query:Yes") Then
ResultString = ResultString.Replace("All_Query:Yes", "")
RTB(ResultString)
End If
threadCount -= 1
Label_T(i.ToString)
End Sub)
End Sub
Private Delegate Sub UpdateStatus(ByVal s As String)
Private Delegate Sub UpdateLabel(ByVal thread_count As String)
Sub RTB(ByVal s As String)
If Me.InvokeRequired Then
Me.Invoke(New UpdateStatus(AddressOf RTB), New Object() {s})
Else
RichTextBox2.AppendText(Environment.NewLine & s)
End If
End Sub
Sub Label_T(ByVal thread_count As String)
If Me.InvokeRequired Then
Me.Invoke(New UpdateLabel(AddressOf Label_T), New Object() {thread_count})
Else
Label3.Text = "Threads Running: " & thread_count
End If
End Sub
End Class