Public Class Form1

  Private Sub Form1_Load(ByVal sender As System.Object, ByVal e _
          As System.EventArgs) Handles MyBase.Load
    tbMainText.Text = _
      "Hallo Leute von heute." & vbNewLine & _
      "Guten Tag. " & vbNewLine & _
      "Heute ist einer von den guten Tagen." & vbNewLine & _
      "Gut, was?" & vbNewLine & _
      "Dies ist GUT so."

    tbSearchText.Text = "Gut"
  End Sub

    'Text suchen in Multiline-TextBox
  Private Sub btnSearch_Click(ByVal sender As System.Object, _
     ByVal e As System.EventArgs) Handles btnSearch.Click

    Dim search As String = ""
    Dim position As Integer
    Dim zeilenummer As Integer

    lstFound.Items.Clear()
    lstLocation.Items.Clear()

     'Multiline-TextBox zeilenweise durchlaufen
    For Each line As String In tbMainText.Lines
      zeilenummer += 1

       'Mit ToLower bei tbSearchText.Text und line wird
       'eine Groß-Klein-Differenzierung verhindert.
      If ckbTextSensitiv.Checked Then
        search = tbSearchText.Text
        position = line.IndexOf(search, 0)
      Else
        search = tbSearchText.Text.ToLower
        position = line.ToLower.IndexOf(search, 0)
      End If

      If position > -1 Then
         'Gefunden in Zeile an Position
        lstLocation.Items.Add("Zeile " & CStr(zeilenummer) & _
          " an Position " & CStr(position))
         'Gefundene Teistrings in Listbox ausgeben
        lstFound.Items.Add(line.Substring(position, search.Length))
      End If
    Next
  End Sub

  Private Sub btnExit_Click(ByVal sender As System.Object, ByVal _
      e As System.EventArgs) Handles btnExit.Click
    Me.Close()
  End Sub

    'Listboxen synchronisieren
  Private Sub lstFound_SelectedIndexChanged(ByVal sender As _
      System.Object, ByVal e As System.EventArgs) Handles _
      lstFound.SelectedIndexChanged
    lstLocation.SelectedIndex = lstFound.SelectedIndex
  End Sub

  Private Sub lstLocation_SelectedIndexChanged(ByVal sender As _
      System.Object, ByVal e As System.EventArgs) Handles _
      lstLocation.SelectedIndexChanged
    lstFound.SelectedIndex = lstLocation.SelectedIndex
  End Sub

End Class