加载GridView中使用cookie值

我有一个方法来载入一个GridView根据内部一个cookie值。
现在，它不加载。请帮我这个cookie

Response.Cookies["selectedDateCookie"].Value = DatePicker.Text;

        Response.Cookies["selectedDateCookie"].Expires = DateTime.Now.AddMinutes(10);

        string selectedDate = Response.Cookies["selectedDateCookie"].Value;

        DataTable  dTable = new DataTable();

        systemBusinessLayer = new BusinessLayer();

        dTable = systemBusinessLayer.GetAllAppointmentsForToday(selectedDate);

        grvViewAppointments.DataSource = dTable;

        grvViewAppointments.DataBind();