导出excel 并且处理长数字，处理科学计数法，以文本形式存储的数字

/// <summary>
        /// 导出Excel文件，并自定义文件名
        /// </summary>
        /// <param name="dtData">数据源</param>
        /// <param name="FileName">导出文件名称</param>
        /// <param name="numberformat">需要处理科学计数法的列的下标</param>
        public static void DataTable3Excel(DataTable dtData, String FileName,string numberformat)
        {
            GridView dgExport = null;
            HttpContext curContext = HttpContext.Current;
            StringWriter strWriter = null;
            HtmlTextWriter htmlWriter = null;

            if (dtData != null)
            {
                curContext.Response.Clear();
                HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8);

                curContext.Response.AddHeader("content-disposition", "attachment;filename="" + System.Web.HttpUtility.UrlEncode(FileName, System.Text.Encoding.UTF8) + ".xls"");
                curContext.Response.ContentType = "application/vnd.ms-excel";
                curContext.Response.Charset = "utf-8";
                curContext.Response.ContentEncoding = System.Text.Encoding.GetEncoding("utf-8");


                strWriter = new StringWriter();
                htmlWriter = new HtmlTextWriter(strWriter);
                dgExport = new GridView();
                dgExport.DataSource = dtData.DefaultView;
                dgExport.AllowPaging = false;
                dgExport.DataBind();
                
                //判断是否存在需要处理科学计数法的列，存在则进行相对应的列的处理，处理为“以文本形式存储的数字”
                if(numberformat!="")
                {
                    string[] arraystr = numberformat.Split(',');
                    foreach (GridViewRow dg in dgExport.Rows)
                    {
                        for (int i = 0; i < arraystr.Length; i++)
                        {
                            dg.Cells[Convert.ToInt32(arraystr[i])].Attributes.Add("style", "vnd.ms-excel.numberformat: @;");
                        }
                    }
                }
                
                dgExport.RenderControl(htmlWriter);
                curContext.Response.Write("<meta http-equiv="content-type" content="application/vnd.ms-excel; charset=utf-8"/>" + strWriter.ToString());
                curContext.Response.End();
            }
        }