MVC3 Html.DropDownList在Html.BeginCollectionItem中使用时不绑定所选值

Question

我在Html.BeginCollectionItem块中使用@ Html.DropDownList时遇到问题。当我创建一个新记录时，我选择的值在HttpPost Action中正确返回。

但是当我尝试编辑现有记录时，视图没有显示DropDownList中当前选定的值。

“编辑”视图呈现部分_EditorForm视图，_EditorForm视图如下所示。

...
@foreach (ContactPhone item in Model.phones)
{
    Html.RenderPartial("_PhoneEditorRow", item);
}
...

_PhoneEditorRow如下

@model CRM.Models.ContactPhone
@using CRM.Helpers;
@{
    Layout = null;
}

<tr class="editor-table-phones-row">
@using (Html.BeginCollectionItem("phones"))
{
    <td valign="top">
        @Html.DropDownListFor(model => model.phoneTypeId, new SelectList(Model.phoneTypes, "id", "name"), "--SELECT--")
        @Html.ValidationMessageFor(model => model.phoneTypeId)
    </td>

    <td valign="top">
        @Html.EditorFor(model => model.phoneNumber)
        @Html.ValidationMessageFor(model => model.phoneNumber)
    </td>

    <td>
        <a href="#" class="delete-table-row">Eliminar</a>
    </td>
}
</tr>

这是ContactPhone类

using System.Collections.Generic;

namespace CRM.Models
{
    public class ContactPhone 
    {
        public long? id { get; set; }

        public PhoneType phoneType { get; set; }

        public byte? phoneTypeId
        {
            get { return this.phoneType.id; }
            set { this.phoneType.id = value; }
        }

        public string phoneNumber { get; set; }

        public List<PhoneType> phoneTypes { get; set; }

        public ContactPhone()
        {
            this.phoneType= new PhoneType();
            this.phoneTypes = new List<PhoneType>();
        }
    }
}

和控制器

...
[Authorize]
public ViewResult Edit(
        int id)
    {
        Contact model = new Contact();

        try
        {
            model = DataProvider.GetContactById(id);
            model.parameters = DataProvider.GetContactParameters();
            this.LoadContactSelectLists(ref model);
        }
        catch (Exception ex)
        {
            ModelState.AddModelError(string.Empty, ex.Message);
        }

        return View(model);
    }
...
private void LoadContactSelectLists(
        ref Contact model)
    {
        if (model.phones.Count > 0)
        {
            List<PhoneType> phoneTypes = DataProvider.GetAllPhoneTypes();
            for (int i = 0; i < model.phones.Count; i++)
                model.phones[i].phoneTypes = phoneTypes;
        }

    }
...