C# / VB.NET - Aprire un file *.txt in una richtextbox

Private Sub Salva_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Salva.Click
        Dim salva As Stream
        SaveFileDialog1.InitialDirectory = "c:\"
        SaveFileDialog1.Filter = "*.txt | *.txt |" & "Tutti i file | *.*"
        SaveFileDialog1.FilterIndex = 2
        SaveFileDialog1.RestoreDirectory = True
        If SaveFileDialog1.ShowDialog() = Windows.Forms.DialogResult.OK Then
                Dim a As New  IO.StreamWriter(OpenFileDialog1.FileName)
                a.Write(rt.Text)
                a.Close()'chiudi a, salva era nel mio esempio..
        End If
    End Sub