怎么保持页面状态

我的主页面有查询条件txtdatestart和 txtdateend和gridview 
在我按照时间段查询后，跳到子页面，在子页面返回到 主页面的时候，主页面保持跳转前的状态（不是初始化的状态）请问这个怎么处理呢？
我代码： if (!IsPostBack)
        {                
            gvShangBB.DataBind();        }public IList MessageList
    {
        get
        {
            IList lstMessage = new ArrayList();           
           
            lstMessage = (new DataUploadManage()).QueryMessageList(GetQueryParam());
          
            return lstMessage;
        }
    } private Hashtable GetQueryParam()
    {
        Hashtable htParam = new Hashtable();
        if (rb1.Checked == true)
        {
            htParam.Add("StartDate", Convert.ToDateTime(DateTime.Now.AddHours(-24)).ToShortDateString());
            htParam.Add("EndDate", Convert.ToDateTime(DateTime.Now).ToShortDateString());
        }
        else
        {
            //判断开始日期和截止日期大小
            if (txtStartDate.Value.Trim() != "" && txtEndDate.Value.Trim() != "")
            {                if (Convert.ToDateTime(txtStartDate.Value.Trim()) > Convert.ToDateTime(txtEndDate.Value.Trim()))
                {
                    htParam.Add("StartDate", Convert.ToDateTime(txtEndDate.Value.Trim()).ToShortDateString());
                    htParam.Add("EndDate", Convert.ToDateTime(txtStartDate.Value.Trim()).ToShortDateString());                }
                else
                {
                    htParam.Add("StartDate", Convert.ToDateTime(txtStartDate.Value.Trim()).ToShortDateString());
                    htParam.Add("EndDate", Convert.ToDateTime(txtEndDate.Value.Trim()).ToShortDateString());
                }
            }
            else 
            {
                if (txtStartDate.Value.Trim() != "")
                {
                    htParam.Add("StartDate", Convert.ToDateTime(txtStartDate.Value.Trim()).ToShortDateString());
                }
                if (txtEndDate.Value.Trim() != "")
                {
                    htParam.Add("EndDate", Convert.ToDateTime(txtEndDate.Value.Trim()).ToShortDateString());
                }
            }
        }
       
        return htParam;
    }