c# 将Datatable数据导出到Excel表格中

public FileResult GetExcelFile()    {      if (Session["beginDate"] != null)      {        string bdate = Session["beginDate"].ToString();        DateTime ld = Convert.ToDateTime(Session["lastDate"].ToString());        DateTime ldate = ld.AddDays(1);        string lldate = ldate.ToString("yyyy-MM-dd");        int ptkey = Convert.ToInt32(Session["Process_PTR"]);        string proceSql = "select * from Assay_Process where RKEY="+ptkey;        DataTable proceDt = SqlHelper.QueryTable(proceSql);        IDataParameter[] iDataTitle = new SqlParameter[3];        iDataTitle[0] = new SqlParameter("@BeginDate", bdate);        iDataTitle[1] = new SqlParameter("@LastDate", lldate);        iDataTitle[2] = new SqlParameter("@RKEY", ptkey);        DataSet dtTitle = SqlHelper.RunProceduresByParameter("pro_GetAssalyInfoByExportPrint", iDataTitle);        DataTable dt = dtTitle.Tables[0];        string outStr = ExcelExport.outExcel(dt);        byte[] fileContents = Encoding.UTF8.GetBytes(outStr.ToString());        return File(fileContents, "application/ms-excel", "" + proceDt.Rows[0]["ProcessName"].ToString().Trim() + "化验单据(" + bdate.Trim() + "-" + lldate.Trim() + ").xls");       }      else      {        string qua_no = Session["quano"].ToString();        IDataParameter[] iDataTitle = new SqlParameter[1];        iDataTitle[0] = new SqlParameter("@Qua_no", qua_no);        DataSet dtTitle = SqlHelper.RunProceduresByParameter("pro_GetAssalyInfoByQua_No", iDataTitle);        DataTable dt = dtTitle.Tables[0];        string outStr = ExcelExport.outExcel(dt);        byte[] fileContents = Encoding.UTF8.GetBytes(outStr.ToString());        return File(fileContents, "application/ms-excel", "化验单据(" + qua_no.Trim()+ ").xls");       }    }