如何在asp.net 3.5中使用自定义代码导出水晶报表

Question

我只想用PDF，EXCEL，WORD等多种选项导出水晶报表。在这里，我提供了如何实现此功能的代码。

//Page Declaration Section
 protected string strQueryString;
    protected int intLastPage;
    protected int intCurPage;

 protected void Page_Init(object sender, System.EventArgs e)
    {
        strQueryString = Request.QueryString.ToString();
        Page.Title = strQueryString.Replace(".rpt", "");
        if (!Page.IsPostBack)
        {
            //Do nothing
        }
        else if (Session[strQueryString] != null)
        {
            CrystalReportViewer1.ReportSource = Session[strQueryString];
        }
    }

 protected void lbut_print_Click(object sender, EventArgs e)
    {
        MPE.Show();
        ......
         reportdocument = new ReportDocument();
            SqlConnectionStringBuilder SConn = new SqlConnectionStringBuilder(conString);
            reportdocument.Load(Server.MapPath(@"~/Admin/PostHistoryReport.rpt"));
            reportdocument.SetDataSource(myDataSet);
            reportdocument.DataSourceConnections[0].SetConnection(SConn.DataSource, SConn.InitialCatalog, SConn.UserID, SConn.Password);
            Session[strQueryString] = reportdocument;
            //Session["SessDoc"] = reportdocument;
            CrystalReportViewer1.ReportSource = reportdocument;
     }

 protected void ImageButton7_Click(object sender, ImageClickEventArgs e)
    {
        if (DDL_ExportOption.SelectedItem.Value != "-1")
        {
            ReportDocument crystalReport = (ReportDocument)Session[strQueryString]; // creating object of crystal report
            switch (DDL_ExportOption.SelectedItem.Value.ToString())
            {
                case "1":
                     crystalReport.ExportToHttpResponse(CrystalDecisions.Shared.ExportFormatType.PortableDocFormat, Response, true, "PostRecordDetails");
                    break;
                case "2":
                    crystalReport.ExportToHttpResponse(CrystalDecisions.Shared.ExportFormatType.ExcelRecord, Response, true,  "PostRecordDetails");
                    break;
                case "3":
                    crystalReport.ExportToHttpResponse(CrystalDecisions.Shared.ExportFormatType.WordForWindows, Response, true, "PostRecordDetails");
                    break;
            }

        }
    }

我怎么得到这个Session[strQueryString]但是这不会给我输出文件。

请帮帮我......