如何在用户控件属性中使用ViewState？

想一次Load后，一直能够使用的全局变量，在回传的时候能够不消失。

结果每次都会重置，查找资料发现需要重写ViewState的一些操作。

        //Persist Viewstate
        protected override void LoadViewState(object savedState)
        {
            object[] viewState = (object[])savedState;
            ArrayList al = viewState[0] as ArrayList;
            if (al != null)
            {
                _formID = (int)al[0];
                _configID = (int)al[1];
                _formPeriodNo = (int)al[2];
                _planPeriodNo = (int)al[3];
                _formMonthStr = (string)al[4];
                _planMonthStr = (string)al[5];
                _webUrl = (string)al[6];
                _isInPeriod = (bool)al[7];
            }
            base.LoadViewState(viewState[1]);
        }
        protected override object SaveViewState()
        {
            if (System.Web.HttpContext.Current == null)
                return null;
            ArrayList al = new ArrayList();
            al.Add(FormID);
            al.Add(ConfigID);
            al.Add(FormPeriodNo);
            al.Add(PlanPeriodNo);
            al.Add(FormMonthStr);
            al.Add(PlanMonthStr);
            al.Add(WebUrl);
            al.Add(IsInPeriod);

            object[] viewState = new object[2];
            viewState[0] = al;
            viewState[1] = base.SaveViewState();
            return viewState;
        }