[C#] - Stampa di un timesheet mensile

    protected void Stampa_Click(object sender, EventArgs e)
    {
        System.IO.StringWriter _sw = new System.IO.StringWriter();
        HtmlTextWriter _hw = new HtmlTextWriter(_sw);

        this.GridView1.RenderControl(_hw);

        Response.Clear();

        Response.ContentType = "application/vnd.ms-excel";
        Response.AppendHeader("Content-Disposition", "attachment; filename=\"Export.xls\"");
        Response.AppendHeader("pragma", "no-cache");
        Response.Buffer = true;
        Response.Expires = -1;

        Response.Write(_sw.ToString());
        Response.Flush();
        Response.End();
    }
    public override void VerifyRenderingInServerForm(Control control)
    {
        // Confirms that an HtmlForm control is rendered for the      
        // specified ASP.NET server control at run time.      
        // No code required here.   
    }

protected void GridView1_RowCreated(object sender, GridViewRowEventArgs e)
{
  if (e.Row.RowType == DataControlRowType.Header)
  {
    e.Row.SetRenderMethodDelegate(new RenderMethod(HeaderRenderMethod));
  }
}

        HtmlTable mytable = new HtmlTable();
        generaHeader(_resultList.Columns, ref mytable);
        generaRighe(_resultList, ref mytable);

 
    private void generaHeader(DataColumnCollection Colonne, ref HtmlTable myTable)
    {
        HtmlTableRow tHead = new HtmlTableRow();
 
        foreach (DataColumn colonna in Colonne)
        {
            string sClass = string.Empty;
            HtmlTableCell tCella = new HtmlTableCell("th");
            tCella.InnerText = colonna.ColumnName;
            tHead.Cells.Add(tCella);
        }
        myTable.Rows.Add(tHead);
    }

    private void generaRighe(DataTable Sorgentedati, ref HtmlTable mytable)
    {
 
        foreach (DataRow row in Sorgentedati.Rows)
        {
            HtmlTableRow tRow = new HtmlTableRow();
 
            string valore = string.Empty;
            string tipo = string.Empty;
            string sClass = string.Empty;
            string colName = string.Empty;

            for (int i = 0; i < row.ItemArray.Length; i++)
            {

                HtmlTableCell tCella = new HtmlTableCell("td");

                valore = row[i].ToString();
                tipo = row[i].GetType().Name;
                colName = Sorgentedati.Columns[i].ColumnName;
                //if (valore != string.Empty)
                //{
                    tCella.InnerText = valore;
                //}
                tRow.Cells.Add(tCella);
            }

            mytable.Rows.Add(tRow);

        }

    }