dropdownlistfor没有在循环中选择正确的值

Question

我有以下代码

public class TestModel
{
   public int TestId1 { get; set; }
   public int TestId2 { get; set; }
   public int TestId3 { get; set; }
   public List<TestSubModel> SubMods { get; set; }

   public IEnumerable<SelectListItem> SelectListItems { get; set; }
}

public class TestSubModel
{
   public string ItemId { get; set; }
}

public class HomeController : Controller
{
   public ActionResult Index()
   {
      var m = new TestModel
      {
         TestId1 = 1,
         TestId2 = 2,
         TestId3 = 3,
         SelectListItems = new List<SelectListItem> { 
                         new SelectListItem { Value = "1", Text = "Item 1" },
                         new SelectListItem { Value = "2", Text = "Item 2" },
                         new SelectListItem { Value = "3", Text = "Item 3" }
                      },
         SubMods = new List<TestSubModel> { 
                         new TestSubModel { ItemId = "1" },
                         new TestSubModel { ItemId = "2" },
                         new TestSubModel { ItemId = "3" }
                      }
      };
      return View(m);
   }
}

和视图：

@model MvcApplication2.Controllers.TestModel

@using (Html.BeginForm())
{
   <ul>
      <li>Test1 Value @Model.TestId1 : @Html.DropDownListFor(i => i.TestId1, Model.SelectListItems)</li>
      <li>Test2 Value @Model.TestId2 : @Html.DropDownListFor(i => i.TestId2, Model.SelectListItems)</li>
      <li>Test3 Value @Model.TestId3 : @Html.DropDownListFor(i => i.TestId3, Model.SelectListItems)</li>
      <li></li>
      @for (var index = 0; index < Model.SubMods.Count(); index++)
      {
         <li>SubModel @index: value @Model.SubMods[index].ItemId
                      @Html.DropDownListFor(i => i.SubMods[index].ItemId, Model.SelectListItems)</li>
      }
   </ul>
}

输出是：

我期望的是项目1，项目2和项目3选择两次。为什么Razor没有在for循环中选择正确的项目？

这也行不通：

@Html.DropDownListFor(i => i.SubMods[index].ItemId, 
                      new SelectList(Model.SelectListItems, "Value", "Text"))

但这样做：

@Html.DropDownListFor(i => i.SubMods[index].ItemId, 
                      new SelectList(Model.SelectListItems, "Value", "Text", Model.SubMods[index].ItemId))

我真的不想每次都创建一个新的选择列表。这是一个错误还是我错过了什么？

我看到this question from 2010但没有回答。