Html.dropdownlist不会在下拉字段中显示默认/选定值

Question

我有一个包含各种行的表,每行对应一个ID.对于每一行,我都有EDIT选项,选中该选项后,用户可以在" Edit.chtml "字段中查看与该ID对应的默认值,然后通过删除默认值并输入新条目来更新它.保存它.

在' Edit.chtml '中,我有一个"MANAGERS"字段,我需要填充一个名称下拉列表,其中显示的默认值/选定值对应于从表中选择编辑操作的行的ID.我正在使用viewBag,但我的问题是下拉列表始终显示列表中的第一项而不是选定的值. 请参阅下面的代码.

Controller:
 //
        // GET: /ManagersNAMES/Edit/5

        public ActionResult Edit(int id)
        {
            using (var db = new InpEntities())
            {
                var list_managers = (from x in db.TABLE_MANAGERS
                                        select new TABLE_MANAGERSDTO
                                        {
                                            ID = x.ID,
                                            NAME = x.NAME,
                                        }).OrderBy(w => w.NAME).ToList();

                ViewBag.managers = new SelectList(list_managers, "ID", "NAME", id);

                return View();
            }
        }

        public class TABLE_MANAGERSDTO
        {
            public string NAME { get; set; }
            public int ID { get; set; }
        }

        //
        // POST: /ManagersNAMES/Edit/5

        [HttpPost]
        public ActionResult Edit(int id, TABLE_INSTITUTES dp)
        {
            try
            {

                using (var db = new InpEntities())
                {

                    TABLE_INSTITUTES tmp = (TABLE_INSTITUTES)db.TABLE_INSTITUTES.Where(f => f.ID == id).First();
                    tmp.MANAGER = dp.MANAGER;
                    db.SaveChanges();
                    return RedirectToAction("Index");
                }
            }
            catch
            {
                return View();
            }
        }

查看:' Edit.chtml '

@{
    ViewBag.Title = "Edit";
}

<h2>Edit</h2>
@using (Html.BeginForm())
{
    @Html.ValidationSummary(true)
    <fieldset>

    <div class="editor-label" style="font-weight:bold">MANAGER</div>
    <div class="editor-field">
        @Html.DropDownList("dp.MANAGER", (SelectList)ViewBag.managers)
    </div>

    <p>
            <input type="submit" value="Save" />
        </p>
    </fieldset>
}

<div>
    @Html.ActionLink("Back to List", "Index")
</div>

Answer 1

您需要在控制器中设置选定的 id，如下所示：

var list_managers =  list_managers.Select(x => new
                          {
                              Value = x.ID.ToString(),
                              Text = x.Name
                          })
                          .ToList();

ViewBag.managers = new SelectList(list_managers, "ID", "NAME", id);

并将您的视图更改为：

@Html.DropDownList("dpMANAGER", (SelectList)ViewBag.managers)