c# – 模型在控制器中接收数据时是否保持其结构？

我有以下ContactUsModel,它是HomeViewModel的一部分,更好地说是单个模型中的嵌套模型类

public class ContactUsDataModel
{
   public string ContactName { get; set; }
   public string ContactEmail { get; set; }
   public string ContactMessage { get; set; }
   public string ContactPhone { get; set; }
}

我在HomeViewModel中获取此模型,如下所示：

public class HomeViewModel
{
   /*My other models goes here*/
   public ContactUsDataModel CUDModel { get; set; }
}

现在在Index.cshtml视图中,我强烈创建了一个表单视图,如下所示：

@model ProjectName.Models.HomeViewModel
<!--I have other views for other models-->
@using (Html.BeginForm("ContactPost","Home",FormMethod.Post,new { id = "contactform" }))
{
    @Html.TextBoxFor(m => m.CUDModel.ContactName,new { @class="contact col-md-6 col-xs-12",placeholder="Your Name *" })
    @Html.TextBoxFor(m => m.CUDModel.ContactEmail,new { @class = "contact noMarr col-md-6 col-xs-12",placeholder = "E-mail address *" })
    @Html.TextBoxFor(m => m.CUDModel.ContactPhone,new { @class = "contact col-md-12 col-xs-12",placeholder = "Contact Number (optional)" })
    @Html.TextAreaFor(m=>m.CUDModel.ContactMessage,placeholder = "Message *" })
    <input type="submit" id="submit" class="contact submit" value="Send message">
 }

我做ajax Post如下：

$('#contactform').on('submit',function (e) {
   e.preventDefault();
   var formdata = new FormData($('.contact form').get(0));
   $.ajax({
            url: $("#contactform").attr('action'),type: 'POST',data: formdata,processData: false,contentType: false,//success
            success: function (result) {
                //Code here
            },error: function (xhr,responseText,status) {
                //Code here
            }
    });
});

在控制器中我试图接收如下：

public JsonResult ContactPost(ContactUsDataModel model)
{
     var name=model.ContactName; //null
     /*Fetch the data and save it and return Json*/
     //model is always null
}

由于某种原因,上述模型始终为null.但是,如果我将模型称为HomeViewModel模型而不是如下所示的控制器参数中的ContactUsDataModel模型,则此方法有效：

public JsonResult ContactPost(HomeViewModel model)
{
     var name=model.CUDModel.ContactName; //gets value
     /*Fetch the data and save it and return Json*/
     //Model is filled.
}

My question here is even though I fill model of type
ContactUsDataModel in the view I am getting it as null if I refer
directly,but ContactUsModel which is inside HomeViewModel gets
filled. Doesn’t type of model matter here. Is the hierarchy its
referred is necessary while fetching in controller?