return_reason_model model = new return_reason_model();
            model.F_RetunrnReason = "1";
            HttpContext.Session["Return"] = model;
            model.F_RetunrnReason = "2";
            return_reason_model model2 = HttpContext.Session["Return"] as return_reason_model;

在上述代碼中，model2.F_RetunrnReason=?? 答案是“2”

           int a = 1;
            HttpContext.Session["Return"] = a;
            a = 2;
            int b = (int)HttpContext.Session["Return"];

在上面代碼中，b=?? 答案是1

當保存在Session中的對象，取出後，在外部發生改變時會怎樣