protected void btnExport_Click(object sender, EventArgs e)
    {
        AsyncExportData Export = new AsyncExportData(this.ExportDataAsync);
        AsyncCallback CallBack = new AsyncCallback(ExportCallBack);
        HttpContext context=this.Context;
        IAsyncResult IAResult = Export.BeginInvoke(context, CallBack, Export);

    }
    //异步导出
    public delegate HSSFWorkbook AsyncExportData(HttpContext context);
    public HSSFWorkbook ExportDataAsync(HttpContext context)
    {
        #region
        //导出方法
        #endregion

        //写入到客户端

        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        book.Write(ms);
        System.Web.HttpContext httpcontext = new HttpContext(context.Request,context.Response);
        try
        {
            httpcontext.Response.AppendHeader("Content-Disposition", string.Format("attachment; filename=" + System.Web.HttpUtility.UrlPathEncode("工单导出列表") + ".xls"));
            httpcontext.Response.BinaryWrite(ms.ToArray());
        }
        catch
        {
            
        }
        book = null;
        ms.Close();
        ms.Dispose();
        return book;
        #endregion
    }
    private void ExportCallBack(IAsyncResult Result)
    {
        AsyncExportData Exoprt = (AsyncExportData)Result.AsyncState;
        HSSFWorkbook book = Exoprt.EndInvoke(Result); 

    }