无法使用Ajax.BeginForm提交模型

Question

我正在尝试在MVC上为ApplicationUsers创建一个更新表单。

这是我的控制者：

   // Usuarios/Modificar
    [HttpPost, ActionName("Modificar")]
    public ActionResult Modificar(ApplicationUser modifiedUser)
    {
        using (ApplicationDbContext db = new ApplicationDbContext())
        {
            var userManager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(db));

            var applicationUser = userManager.FindById(modifiedUser.Id);

            if (applicationUser != null)
            {
                applicationUser.Apellido = modifiedUser.Apellido;
                applicationUser.Nombre = modifiedUser.Nombre;
                applicationUser.Dni = modifiedUser.Dni;
                applicationUser.Interno = modifiedUser.Interno;
                applicationUser.Email = modifiedUser.Email;
                applicationUser.UserName = modifiedUser.UserName;

                userManager.Update(applicationUser);
            }
        }

        return null;
    }

这是我的观点：

@model Core.Models.ApplicationUser

@using (Ajax.BeginForm("Modificar", "Usuarios", new AjaxOptions(){ HttpMethod = "POST", }))
{
    @Html.ValidationSummary(true, "", new { @class = "text-danger" })
    @Html.HiddenFor(model => model.Id)

    <div class="col-md-12">
        <div class="box box-default">

            <!-- #region Header del Box -->
            <div class="box-header with-border">
                <h3 class="box-title">Usuario: @Model.UserName</h3>
            </div>
            <!-- #endregion -->

            <!-- #region Cuerpo del box. -->
            <div class="box-body">
                <!-- #region Fila 1. -->
                <div class="row">
                    <!-- Columna 1. -->
                    <div class="col-md-2">
                        <div class="form-group">
                            <i class="fa fa-fw fa-user"></i> <label>Apellido: </label>
                            @Html.EditorFor(model => model.Apellido, new {htmlAttributes = new {@class = "form-control"}})
                            @Html.ValidationMessageFor(model => model.Apellido, "", new {@class = "text-danger"})

                        </div>
                    </div>
                    <!-- /.col -->
                    <!-- Columna 2. -->
                    <div class="col-md-2">
                        <div class="form-group">
                            <i class="fa fa-fw fa-user"></i> <label>Nombre: </label>
                            @Html.EditorFor(model => model.Nombre, new {htmlAttributes = new {@class = "form-control"}})
                            @Html.ValidationMessageFor(model => model.Nombre, "", new {@class = "text-danger"})
                        </div>
                    </div>
                    <!-- /.col -->
                    <!-- Columna 3. -->
                    <div class="col-md-2">
                        <div class="form-group">
                            <i class="fa fa-fw fa-user"></i> <label>Documento: </label>
                            @Html.EditorFor(model => model.Dni, new {htmlAttributes = new {@class = "form-control"}})
                            @Html.ValidationMessageFor(model => model.Dni, "", new {@class = "text-danger"})
                        </div>
                    </div>
                    <!-- /.col -->
                    <!-- Columna 4. -->
                    <div class="col-md-2">
                        <div class="form-group">
                            <i class="fa fa-fw fa-user"></i> <label>Mail: </label>
                            @Html.EditorFor(model => model.Email, new {htmlAttributes = new {@class = "form-control"}})
                            @Html.ValidationMessageFor(model => model.Email, "", new {@class = "text-danger"})
                        </div>
                    </div>
                    <!-- /.col -->
                    <!-- Columna 5. -->
                    <div class="col-md-2">
                        <div class="form-group">
                            <i class="fa fa-fw fa-user"></i> <label>Usuario: </label>
                            @Html.EditorFor(model => model.UserName, new { htmlAttributes = new { @class = "form-control" } })
                            @Html.ValidationMessageFor(model => model.Email, "", new { @class = "text-danger" })
                        </div>
                    </div>
                    <!-- /.col -->
                </div>
                <!-- #endregion /.row -->

            </div>
            <!-- #endregion /.box-body -->

            <div class="box-footer">
                <div class="row">
                    <div class="col-md-1 pull-right">

                        <input type="submit" name="btnAppUser" id="btnAppUser" class="btn btn-default pull-right" value="Guardar" />
                    </div>
                </div>
            </div>
        </div>    
</div>
}

但是，提交后，当帖子到达控制器时，applicationUser为空。 Ajax表单不是发送信息，也不是绑定到ApplicationUser模型。谁能帮我理解这个问题呢？

谢谢！