ASP Web窗体：应将绑定项放在哪里？

Question

I'd like to bind a List<StockInList> to a GridView , show them to user, and get them back(perhaps user will edit them) to do something else. However, when I retrieved the bound item stockInLists , it's null . Reason I guess is that ASP create a new Code-Behind class Add_Inventories to handle request, so I lost the access to my bound item stockInLists .

Am I doing something wrong? What should I do to get them back correctly?

 public partial class Add_Inventories : System.Web.UI.Page
    {
        private ShoppingDbContext shoppingDbContext = new ShoppingDbContext();

        private List<StockInList> stockInLists;

        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {

       var        stockInListsFromSession =(List<StockInList>)Session["stock_in_list"]; 
                if (stockInListsFromSession != null)
                {
//save the stockInLists in private filed, so that I can get them back, however it's null when method `Add()` invoke. 
                    stockInLists=new List<StockInList>(stockInListsFromSession);

                    GridView1.DataSource = stockInLists;
                    GridView1.DataBind();
                }
                else
                {
                   //...
                }
            }
        }


        protected async void Add(object sender, EventArgs e)
        {



            foreach (var stockInList in stockInLists)
            {
            shoppingDbContext.StockInLists.Add(stockInList);
            }

            await shoppingDbContext.SaveChangesAsync();


            Response.Redirect(Request.Url.AbsoluteUri);
        }


    }

Answer 1

The data in variables are lost when page is refreshed(Scope), to prevent it we should use Sessions, viewstate etc or make that variable as static(Not recommended).

In your case value stored in stockInLists will be lost if the page is refreshed,

• store its data in viewstate ViewState["stockInLists"] = stockInLists;
• store its data in Session Session("stockInLists") = stockInLists; (Recommended)
• make it a static variable private List<StockInList> stockInLists; (Not Recommended)

I hope you understand it :)