全局变量问题，高手指点

                   DEC.Objects.MaterialStock objMaterialStock = new DEC.Objects.MaterialStock();
                    objMaterialStock.StockState = 0;
                    objMaterialStock.CreateDate = Convert.ToDateTime(DateTime.Now.ToShortDateString());
                    if (ViewState["objlist"] != null) 
                    {
                        objlist = (List<DEC.Objects.MaterialStock>)ViewState["objlist"];
                    }
                    objlist.Add(objMaterialStock);
                    ViewState["objlist"] = objlist;