c# - HtmlTextWriter asp.net c# webformに文字列を追加する方法

Question

オプションタグを文字列として返す以下のような関数があるとしましょう。

 public static string writeDropDownOptionHTML(string tablename, string id_col, string value_col)
        {
            StringWriter stringwriter = new StringWriter();
            HtmlTextWriter writer = new HtmlTextWriter(stringwriter);
            DataTable dt1 = BAL.setDropDown(tablename, id_col, value_col);
            if (dt1.Rows.Count > 0)
            {
                foreach (DataRow row in dt1.Rows)
                {
                    writer.AddAttribute(HtmlTextWriterAttribute.Value, row[0].ToString());
                    writer.RenderBeginTag(HtmlTextWriterTag.Option);

                    writer.Write(row[1].ToString());
                    writer.RenderEndTag();
                }
            }

            return stringwriter.ToString();
        }

今、私は以下のような別の機能を持っています

public static string writeWalkReverseTableData(DataTable dt1)
        {
            StringWriter stringwriter = new StringWriter();
            HtmlTextWriter writer = new HtmlTextWriter(stringwriter);

            if (dt1.Rows.Count > 0)
            {
                foreach (DataRow row in dt1.Rows)
                {

                    writer.RenderBeginTag(HtmlTextWriterTag.Tr);
                    writer.RenderBeginTag(HtmlTextWriterTag.Td);
                    writer.RenderBeginTag(HtmlTextWriterTag.Select);
                    // now i want to call  writeDropDownOptionHTML which will return option html code
                    // writer += writeDropDownOptionHTML("xyz","abc","def"); 
                    writer.RenderEndTag();
                    writer.RenderEndTag();
                    writer.RenderEndTag();
                }
            }
            return stringwriter.ToString();
        }

HtmlTextWriterに文字列を追加する方法は?