How to capture all the comments from class files (.cs) using C#?

  private void button1_Click(object sender, EventArgs e)
        {
            List lst = new List();  
            openFileDialog1.ShowDialog();
            textBox1.Text = openFileDialog1.FileName;

            using (StreamReader sr = new StreamReader(textBox1.Text))
            {
                String line;              
                while ((line = sr.ReadLine()) != null)
                {
                    if (line.Trim().StartsWith("//"))
                    {
                        lst.Add(line + "\n");
                    }
                }
            }
           using (StreamWriter outfile = new StreamWriter("D:\\" + "Comments_logger.txt"))
            {
                foreach (string str in lst)
                {
                    outfile.Write(str + "\n");
                }
            }       

        }