Highlighting text when searching for it in vb.net - vb.net

Question

Hi so I've created a search system with a button, textbox and rich text box to search for items displayed in the rich text box (which are imported from a text file) and to highlight them when found. For some reason when I click the search button, it does not highlight the word that is being searched for.
This is the code I used:
Private Sub btnSearch_Click(sender As Object, e As EventArgs) Handles btnSearch.Click
Dim index As Integer = 0
While index < rtxtEdit.Text.LastIndexOf(txtSearch.Text)
rtxtEdit.Find(txtSearch.Text,index ,rtxtEdit.TextLength, RichTextBoxFinds.None)
rtxtEdit.SelectionBackColor = Color.Red
index = rtxtEdit.Text.IndexOf(txtSearch.Text, index) + 1
End While
End Sub

Answer 1

As stated in this post:
Private Sub btnSearch_Click(sender As Object, e As EventArgs) Handles btnSearch.Click
Dim len = searchText.Length
Dim pos = rtb.Find(searchText, 0, RichTextBoxFinds.NoHighlight)
While (pos >= 0)
rtb.Select(pos, len)
rtb.SelectionBackColor = Color.Yellow
if pos + len >= rtb.Text.Length Then
Exit While
End If
pos = rtb.Find(searchText, pos + len, RichTextBoxFinds.NoHighlight)
End While
End Sub

Answer 2

I'd write that this way instead:
Private Sub btnSearch_Click(sender As Object, e As EventArgs) Handles btnSearch.Click
Dim searchFor As String = txtSearch.Text.Trim
If searchFor <> "" Then
Dim index As Integer = 0
Dim startAt As Integer = 0
Do
index = rtxtEdit.Find(searchFor, startAt, RichTextBoxFinds.None)
If index <> -1 Then
rtxtEdit.SelectionBackColor = Color.Red
startAt = index + 1
End If
Loop While index <> -1
End If
End Sub

Answer 3

Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim index As Integer = 0
'Clears the existing formatting
Dim t = rtxtEdit.Text
rtxtEdit.Text = t
'Incremented the loop condition by 1 so that text at the beginning gets selected as well.
While index < rtxtEdit.Text.LastIndexOf(txtSearch.Text) + 1
rtxtEdit.Find(txtSearch.Text, index, rtxtEdit.TextLength, RichTextBoxFinds.None)
rtxtEdit.SelectionBackColor = Color.Red
index = rtxtEdit.Text.IndexOf(txtSearch.Text, index) + 1
End While
End Sub