Dim sr As New IO.StreamWriter("\My Documents\testordner\Barcodes.txt", True, _
   True)
 sr.WriteLine(TextBox1.Text)
 sr.Flush()
 sr.Close()

        Dim fileCount As Integer
        '###Die Nummerierung der zuletzt gespeicherten Datei auslesen###
        For Each fl As String In IO.Directory.GetFiles("\My" & _
          "Documents\testordner", "Barcode*.txt")
            Dim aktCount As Integer = Val(Replace(Replace(Replace(fl, "\My" & _
            "Documents\testordner\", String.Empty), "Barcode", String.Empty), _
            ".txt", String.Empty))
            If aktCount > fileCount Then fileCount = aktCount
        Next
        '###############################################################
        Dim sr As New IO.StreamWriter("\My Documents\testordner\Barcode" & _
          fileCount + 1 & ".txt", True, True)
        sr.WriteLine(TextBox1.Text)
        sr.Flush()
        sr.Close()