Asp.net MVC 3：控制器中的模型是空的吗？

所以这就是我所做的：

创建了一个视图模型：

public class EntityChooserModel
    {
        public IEnumerable<Entity> AvailableEntities { get; set; }
        public int SelectedId;
    }

我在控制器中有两个动作,一个是[HTTPPost],一个没有.在两者中我都有一个“SessionUserData”,它是会话数据,通过数据模型绑定绑定.

[Authorize]
        public ActionResult EntityChooser(SessionUserData sessionData)
        {
            List<Entity> entities = _userStore.GetRoles(User.Identity.Name).Select(ur => ur.Entity).ToList();


            Entity entity = sessionData.IdCurrentEntity != null ? entities.Where(e => e.Id == sessionData.IdCurrentEntity).First() : entities.First();

            return View(new EntityChooserModel() { SelectedId = entity.Id,AvailableEntities = entities });
        }

.

[Authorize]
    [HttpPost]
    public ActionResult EntityChooser( EntityChooserModel model,SessionUserData sessionData,String returnUrl)
    {
        if (ModelState.IsValid)
        {
            Entity entity = _userStore.GetRoles(User.Identity.Name).Select(ur => ur.Entity).Where(e => e.Id == model.SelectedId).First();
            sessionData.IdCurrentEntity = entity.Id;
            RedirectToDefaultPage(returnUrl);
        }
        return View(model);
    }

强类型视图：

@model My.Full.Namespace.EntityChooserModel
@{
    ViewBag.Title = "EntityChooser";
    Layout = "~/Views/Shared/_LoginLayout.cshtml";
}
<div id="login-wrapper">
    <div id="title">
        <h1>Login</h1>
    </div>
    <div id="login">
        @using (Html.BeginForm("EntityChooser","Auth",FormMethod.Post,new { id = "ChooseFormId" }))
        {            
            @Html.ValidationSummary(true,"Loggin error")
            <div>
                <span>Choose an entity:</span>
                @Html.DropDownListFor(x => x.SelectedId,new SelectList(Model.AvailableEntities,"Id","Name"))
            </div>
            <p class="right-aligned">
                <a href="javascript:document.getElementById('ChooseFormId').submit();" class="adm-button">
                    <span class="next-btn"><span>Select</span></span></a>
            </p>
            <input type="submit" style="display: none" />
        }
    </div>
</div>

问题是,当我在第二个模型中收到数据时,我有一个空对象.该集合为空,id设置为默认值(0).

怎么了？我无法找到我在这个上错过的东西.

这是我第一次做一个不是ForModel()的mvc表单,而且我第一次使用下拉列表