Adding Template Field to Gridview Programmatically

 private void SetInitialRow()
        {
            DataTable dt = new DataTable();

                if (ddlBroker.SelectedIndex > 0 && ViewState["CurrentTable"] == null) 
                {
                    objBEL.Broker_id = int.Parse(ddlBroker.SelectedValue.ToString());
                    objBEL.city_id = objBLL.GetCityId(objBEL);
                    dt = objBLL.GetRecords(objBEL);

     
                    if (dt.Rows.Count > 0)
                    {

                        DataRow dr = null;

                        gdvRates.DataSource = ViewState["CurrentTable"];
                        gdvRates.DataBind();

                        dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));
                        dr = dt.NewRow();
                        dr["RowNumber"] = 1;
                        dr["Subcommodity_name"] = string.Empty;
                        dr["City_name"] = string.Empty;
                        dr["Brand_Name"] = string.Empty;
                        dr["Brand_Desc"] = string.Empty;
                        dr["Min_Rate"] = DBNull.Value;
                        dr["Max_Rate"] = DBNull.Value;
                        dr["Brand_Abbr"] = string.Empty;
                        dr["Brand_Id"] = DBNull.Value;
                        dr["Rate_id"] = DBNull.Value;

                        dt.Rows.Add(dr);

                        ViewState["CurrentTable"] = dt;

                        gdvRates.DataSource = ViewState["CurrentTable"];
                        gdvRates.DataBind();


                    }
                }

                else
                {
                    DataRow dr = null;
dt = (DataTable)ViewState["CurrentTable"];

                 //   gdvRates.DataSource = ViewState["CurrentTable"];
                  //  gdvRates.DataBind();

                    dt.Columns.Add(new DataColumn("RowNumber", typeof(string)));
                    dt.Columns.Add(new DataColumn("Subcommodity_name", typeof(string)));
                    dt.Columns.Add(new DataColumn("City_name", typeof(string)));
                    dt.Columns.Add(new DataColumn("Brand_Name", typeof(string)));
                    dt.Columns.Add(new DataColumn("Brand_Abbr", typeof(string)));
                    dt.Columns.Add(new DataColumn("Brand_Desc", typeof(string)));
                    dt.Columns.Add(new DataColumn("Min_Rate", typeof(string)));
                    dt.Columns.Add(new DataColumn("Max_Rate", typeof(string)));
                    dt.Columns.Add(new DataColumn("Brand_Id", typeof(string)));
                    dt.Columns.Add(new DataColumn("Rate_id", typeof(string)));

                    dr = dt.NewRow();
                    dr["RowNumber"] = 1;
                    dr["Subcommodity_name"] = string.Empty;
                    dr["City_name"] = string.Empty;
                    dr["Brand_Name"] = string.Empty;
                    dr["Brand_Desc"] = string.Empty;
                    dr["Min_Rate"] = DBNull.Value;
                    dr["Max_Rate"] = DBNull.Value;
                    dr["Brand_Abbr"] = string.Empty;
                    dr["Brand_Id"] = DBNull.Value;
                    dr["Rate_id"] = DBNull.Value;

                    dt.Rows.Add(dr);

                    ViewState["CurrentTable"] = dt;

                    gdvRates.DataSource = ViewState["CurrentTable"];
                    gdvRates.DataBind();


                }
                       
        }