Get String Between Characters (Tags)

Public Class Form1
    Private sessionKey as string = nothing
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click


        sessionKey = GetStringBetweenTags("<session_key>", "</session_key>", textbox1.text)


    End Sub

    Private function GetStringBetweenTags(ByVal startIdentifer As String, ByVal endIndentifier As String, ByVal textsource As String) as string
        Dim idLength As Int16 = startIdentifer.Length

        Dim s As String = textsource

        Try

            s = s.Substring(s.IndexOf(startIdentifer) + idLength)
            s = s.Substring(0, s.IndexOf(endIndentifier))
            'MsgBox(s)

        Catch
        End Try
return s
    End Sub
End Class