C# userControl LoadControl 動態載入並存在Session

if (Session["c3"] == null)
            {
                c3 = LoadControl("_UC/Uc_aaaa.ascx");
                Session["c3"] = c3;
            }
            else
            {
                c3 = (Control)Session["c3"];
            }
            Panel2.Controls.Add(c3);