mvc 2 中的编辑模式下下拉列表不显示所选值

Question

您好，我试图在编辑部分的下拉列表上显示数据库值，但下拉列表显示以下默认设置值是我的代码： 控制器：

 public ActionResult Edit(int id)
    {
       // Product helmet = new Product();//
        //Product garrage = new Product();

        ViewBag.mode = "edit";
        // for dropdown track
        ITrackRepository trackResp = new TrackRepository();
        IQueryable<Object> tracks = trackResp.GetVenuesSelectlist();
        ViewData["Venue"] = new SelectList(tracks, "VenueID", "Name");

        // for dropdown for event type
        ITrackdayRepository trackdayResp = new TrackdayRepository();
        IQueryable<EventType> eventTypes = trackdayResp.GetAllEventTypes();
        ViewData["EventTypes"] = new SelectList(eventTypes, "ID", "Name");

        // for dropdown experience
        IExperienceLevelRepository expLevelResp = new ExperienceLevelRepository();
        IQueryable<ExperienceLevel> expLevel = expLevelResp.GetAllExperienceLevels().OrderBy(ExperienceLevel => ExperienceLevel.Name);
        ViewData["Experience"] = new SelectList(expLevel, "ID", "Name");

        // dropdown for helmets
        IProductRepository prodResp = new ProductRepository();
        Product productQuantity = prodResp.GetProd(id);

        if (productQuantity.ProductTypeID == 1)
        {
            // dropdown for attendees
            var attendees = Enumerable.Range(1, 80).Select(x => new SelectListItem { Value = x.ToString(), Text = x.ToString() });
            ViewData["attendees1"] = new SelectList(attendees, "Value", "Text",**productQuantity.QtyAvailable)**; //productQuantity.QtyAvailable is the value from db(selected value of dropdown)

            ViewData["txtAttendees"] = productQuantity.UnitCost;
        }


        else
        {
            var emptyattendees = Enumerable.Range(1, 80).Select(x => new SelectListItem { Value = x.ToString(), Text = x.ToString() });
            ViewData["attendees1"] = new SelectList(emptyattendees.ToList(), "Value", "Text");


        }    Event trackday = trackdayResp.GetEvent(id); //returns all the values from event table whose eventid is id

        //need to return product quantity, value to drop downlist
       return View("Create", trackday);

    }

查看已编辑（工作）：

  <% if (ViewBag.mode != "edit")
                  { %>

                <%: Html.DropDownList("attendees1", ViewData["attendees1"] as SelectList, "--select--")%>
               <%}else{%>
               <%: Html.DropDownList("attendees1")%>
               <%} %>

Answer 1

一个月前我遇到了同样的问题，我通过这样做解决了它：

ViewData["attendees1"] = new SelectList(attendees, "Value", "Text", productQuantity.QtyAvailable);

我的意思是，您必须使用 SelectedValue 添加第四个参数，您可以在编辑之前从原始值中获取它。您只需在“编辑”操作中执行此操作，无需在“创建”中执行此操作，因为它是一个新对象并且尚未选择任何值。

在您的标记中，您可以像这样定义 DropDownList：

<%: Html.DropDownList("attendees1") %>

这样，将选择所选值而不是默认值。

希望有帮助。

编辑：
创建操作方法：

ViewData["attendees1"] = new SelectList(attendees, "Value", "Text");

编辑操作方法：

ViewData["attendees1"] = new SelectList(attendees, "Value", "Text", productQuantity.QtyAvailable);

在创建和编辑视图中进行标记

<%: Html.DropDownList("attendees1") %>