为什么提交按钮从视图传递空数据到控制器

我是c#和MVC的新手，这可能看起来像一个基本的问题，但即使在彻底搜索了有类似问题的人之后，我也不能使这个工作。

问题是在一个提交按钮上，我有一个编辑视图，由于某种原因传递null数据到更新方法，而不是表单输入数据。

这是视图:

<div class="row-fluid metro">
<div class="span2 offset4">
    @using (Html.BeginForm("Update", "Realty", FormMethod.Post))
    {
        @Html.HiddenFor(model => model.Address)
        @Html.HiddenFor(model => model.Details)
        @Html.HiddenFor(model => model.Manager)
        @Html.ValidationSummary(true)
        <div class="control-group">
            <label class="control-label">Details</label>
            <div class="controls">
                @Html.EditorFor(model => model.Details)
                @Html.ValidationMessageFor(model => model.Details)
            </div>
        </div>
        <div class="control-group">
            <label class="control-label">Address</label>
            <div class="controls">
                @Html.EditorFor(model => model.Address)
                @Html.ValidationMessageFor(model => model.Address)
            </div>
        </div>

        <div class="control-group">
            <label class="control-label">Manager</label>
            <div class="controls">
                  @Html.DropDownListFor(model => model.Manager.Id, Model.Managers)
               </div>
        </div>

        <div class="form-actions">
            <button type="submit" class="btn btn-primary">Guardar</button>
            <a href="@Url.Action("Index", "Realty")"><button type="button" class="btn">Cancelar</button></a>
        </div>
    }
</div>

这是视图模型公共类RealtyViewModel｛//////获取或设置id。///公共int Id{获取;设置;}

    public string Address { get; private set; }
    /// <summary>
    /// Gets the details.
    /// </summary>
    public string Details { get; private set; }
    public List<HomeViewModel> Homes { get; private set; }
    /// <summary>
    /// Gets the manager.
    /// </summary>


    public IEnumerable<SelectListItem> Managers { get; set; }
    public ManagerViewModel Manager { get; private set; }
    public RealtyViewModel(int id,string Address, string Details, ManagerViewModel Manager)
    {
        this.Id = id;
        this.Address = Address;
        this.Details = Details;
        this.Manager = Manager;
    }
    public RealtyViewModel() {}
}

}

最后，如果需要的话，这是来自控制器的Update方法:

            public ActionResult Update(RealtyViewModel model)
    {
        if (model.Id == 0)
        {
            var manager = this.managerService.Get(model.Manager.Id);
            this.realtyService.Create(model.Address, model.Details,manager);
        }
        else
        {
            var manager = this.managerService.Get(model.Manager.Id);
            this.realtyService.Update(model.Id,model.Address, model.Details, manager);
        }
        return this.RedirectToAction("Index");
    }

任何帮助都将是感激的，提前感谢。

         public ActionResult Edit(int id)
    {
        List<SelectListItem> managers = new List<SelectListItem>();
        var model = new RealtyViewModel();
        if (id != 0)
        {
            var realty = this.realtyService.Get(id);
            var mvm = new ManagerViewModel(realty.Manager.Id, realty.Manager.Name, realty.Manager.Age);
            model = new RealtyViewModel(realty.Id, realty.Address, realty.Details, mvm);
        }
        foreach (var Manager in managerService.GetAll())
        {
            managers.Add(new SelectListItem { Value=Manager.Id.ToString(),Text=Manager.Name});
        }
        model.Managers = managers;
        return this.View(model);
    }

<div class="row-fluid metro">
<div class="span2 offset4">
    @using (Html.BeginForm("Update", "Realty", FormMethod.Post))
        {
        @Html.ValidationSummary(true)
            <div class="control-group">
            <label class="control-label">Details</label>
            <div class="controls">
                @Html.EditorFor(model => model.Details)
                @Html.ValidationMessageFor(model => model.Details)
            </div>
        </div>
        <div class="control-group">
            <label class="control-label">Address</label>
            <div class="controls">
                @Html.EditorFor(model => model.Address)
                @Html.ValidationMessageFor(model => model.Address)
            </div>
        </div>

        <div class="control-group">
            <label class="control-label">Manager</label>
            <div class="controls">
                  @Html.DropDownListFor(model => model.Manager.Id, Model.Managers)
               </div>
        </div>

        <div class="form-actions">
            <button type="submit" class="btn btn-primary">Guardar</button>
            <a href="@Url.Action("Index", "Realty")"><button type="button" class="btn">Cancelar</button></a>
        </div>
    }
</div>