NPOI导出EXCEL报_服务器无法在发送 HTTP 标头之后追加标头

/// <summary>
    /// EXCEL帮助类
    </summary>
    <typeparam name="T">泛型类</typeparam>
    <typeparam name="TCollection">泛型类集合</typeparam>
    public class ExcelHelp<T,TCollection> where TCollection : List<T>
    {
        static ExcelHelp<T,TCollection> instance = new ExcelHelp<T,TCollection>();
        //获取httpResponse对象原位置，放在这里不知道会报错：服务器无法在发送 HTTP 标头之后追加标头
        可能是这里拿到的httpResponse对象不是最新请求的对象导致的，将其放到方法内部即可
        HttpResponse baseResponse = HttpContext.Current.Response;

        <summary>
         将数据导出EXCEL
        </summary>
        <param name="columnNameAndShowNameDic">键值对集合（键：列名，值：每列数据集合）</param>
        void ExportExcelData(Dictionary<string,List<string>> columnNameAndShowNameDic)
        {
            IWorkbook workbook = new HSSFWorkbook();
            ISheet worksheet = workbook.CreateSheet("sheet1");


            List<string> columnNameList = columnNameAndShowNameDic.Keys.ToList();
            设置首列显示
            IRow row1 = worksheet.CreateRow(0);
            ICell cell = null;
            ICellStyle cellHeadStyle = workbook.CreateCellStyle();
            设置首行字体加粗
            IFont font = workbook.CreateFont();
            font.Boldweight = short.MaxValue;
            cellHeadStyle.SetFont(font);
            for (var i = 0; i < columnNameList.Count; i++)
            {
                cell = row1.CreateCell(i);
                cell.SetCellValue(columnNameList[i]);
                cell.CellStyle = cellHeadStyle;
            }
            var raws = columnNameAndShowNameDic[columnNameList[]].Count;
            int i = )
            {
                int j = 0; j < raws; j++)
                {
                    if (i == )
                    {
                        row1 = worksheet.CreateRow(j + 1);
                    }
                    else
                    {
                        row1 = worksheet.GetRow(j + );
                    }
                    cell = row1.CreateCell(i);
                    cell.SetCellValue(columnNameAndShowNameDic[columnNameList[i]][j]);
                }
                设置行宽度自适应
                worksheet.AutoSizeColumn(i,true);
                worksheet.SetColumnWidth(i,columnWidth * 200);
            }
            http请求Response对象-这里httpResponse对象要在方法内获取，否则可能会出现：无法再response发送表头后添加header的问题
            HttpResponse baseResponse = HttpContext.Current.Response;
            baseResponse.Clear();
            baseResponse.Buffer = ;
            baseResponse.ContentEncoding = System.Text.Encoding.UTF8;
            baseResponse.ContentType = application/vnd.ms-excel;
            设置导出文件名
            baseResponse.AppendHeader(content-disposition",attachment;filename=zhilian.xls);
            MemoryStream ms =  MemoryStream();
            workbook.Write(ms);
            byte[] buffer = ms.ToArray();
            baseResponse.AddHeader(Content-Length,buffer.Length.ToString());
            baseResponse.BinaryWrite(buffer);
            baseResponse.Flush();
            baseResponse.End();
        }
    }