C# Crystal report无法在静态功能下工作

我正在使用crystal report并从存储过程中获取数据，但当在page onload函数中使用此函数时，它将以正确的方式工作，而不是在静态函数中，它在最后一行显示错误：“对象引用未设置为对象的实例

    public static void DrawGrids()
        {
            ReportDocument rptDoc = new ReportDocument();
            ComplaintTrackingSystem.Reports.Datas dss = new Reports.Datas();
            DataTable dt = new DataTable();
            DataSet ds;
            Hashtable ObjParameters = new Hashtable();
            BusinessLogicLayer ObjBusiness = new BusinessLogicLayer();
            ds =ObjBusiness.SPDataSet(ObjParameters,"SelectUserComplaintsByComptIdReport");
            dt.TableName = "Crystal Report Example";
            dt = ds.Tables[0]; //This function is located below this function
            dss.Tables[0].Merge(dt);
rptDoc.Load(HttpContext.Current.Server.MapPath("../Reports/ComplaintReport.rpt"));
            //set dataset to the report viewer.
            rptDoc.SetDataSource(dss);
            CrystalDecisions.Web.CrystalReportViewer obj = new CrystalDecisions.Web.CrystalReportViewer();
            Page p = HttpContext.Current.Handler as Page;
            obj = (CrystalDecisions.Web.CrystalReportViewer)p.FindControl("CrystalReportViewer1");
            obj.ReportSource = rptDoc; 
        }

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您在哪一行得到错误？obj.ReportSource=rptDoc；