Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button2.Click
        Dim sr As New System.IO.StreamReader("C:\test.txt", _
        System.Text.Encoding.Default)
        Dim s() As String = Split(sr.ReadToEnd(), ",")
        sr.Close()
        ListBox1.DataSource = s
    End Sub
 
    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button3.Click
        Dim sw As New System.IO.StreamWriter("C:\test1.txt", False, _
        System.Text.Encoding.Default)
        Dim s(ListBox1.Items.Count - 1) As String
        ListBox1.Items.CopyTo(s, 0)
        sw.Write(Join(s, ","))
        sw.Close()
    End Sub