从编辑返回ViewModel时出现问题

我试图将相同的模型返回到编辑模型的视图中。使它有点像Word或者其他一些带有ctrl+s功能的东西来保存模式。尽管由于某些愚蠢的原因,返回到视图的模型包含了一堆空值,但这仍然可以正常工作。是因为当控制器取回视图模型时没有正确序列化,还是我处理MVC的方式不对?

这就是模型

public class EditInvoiceModel
{
    private readonly IEnumerable<Customer> _customers;

    public EditInvoiceModel()
    {
        CreateProduct = new Product { Invoice = Invoice };
        CreateWorkday = new Workday { Invoice = Invoice };
    }

    public EditInvoiceModel(Invoice invoice, IEnumerable<Customer> customers)
    {
        Invoice = invoice;
        _customers = customers;

        Customers = _customers.Select(x =>
                                      new SelectListItem
                                        {
                                            Selected = x.Id == Invoice.CustomerID,
                                            Text = x.Name,
                                            Value = x.Id.ToString()
                                        });

        Products = Invoice.Products;
        Workdays = Invoice.Workdays;

        CreateProduct = new Product {Invoice = Invoice};
        CreateWorkday = new Workday { Invoice = Invoice };
    }

    public IEnumerable<SelectListItem> Customers { get; set; }
    public IEnumerable<Product> Products { get; set; }
    public IEnumerable<Workday> Workdays { get; set; }
    public Product CreateProduct { get; set; }
    public Workday CreateWorkday { get; set; }
    public Invoice Invoice { get; set; }
}

[AcceptVerbs(HttpVerbs.Post)]
public ActionResult Edit(EditInvoiceModel invoiceModel)
{
    try
    {
        _repository.UpdateInvoice(invoiceModel.Invoice);
    }
    catch (Exception ex)
    {
        Log.Error(ex);
    }

    return View(invoiceModel);
}

当发票返回到视图时,除发票之外的所有属性都为空。我不知道为什么会这样。希望有人能帮忙。

The ViewData item that has the key 'Invoice.CustomerID' is of type 'System.Int32' but must be of type 'IEnumerable<SelectListItem>'.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. 
Exception Details: System.InvalidOperationException: The ViewData item that has the key 'Invoice.CustomerID' is of type 'System.Int32' but must be of type 'IEnumerable<SelectListItem>'.

Source Error: 

Line 28:        <div class="editor-field">
Line 29:            <%: Html.DropDownListFor(x => x.Invoice.CustomerID, Model.Customers)%>
Line 30:            <%: Html.ValidationMessageFor(x => x.Invoice.CustomerID)%>
Line 31:        </div>

显示视图模型的视图的最后一部分。

<%@ page language="C#" masterpagefile="~/Views/Shared/Site.Master" 
    inherits="System.Web.Mvc.ViewPage<FakturaLight.WebClient.Models.EditInvoiceModel>" %>
<asp:content id="Content2" contentplaceholderid="MainContent" runat="server">
    <%= Html.ValidationSummary() %>
    <% using (Html.BeginForm())
    { %>
    <%= Html.AntiForgeryToken() %>
    <div class="content-left">
        <%: Html.EditorFor(x => x.Invoice) %>
        <div class="editor-label">
            <%: Html.LabelFor(x => x.Invoice.CustomerID)%>
        </div>
        <div class="editor-field">
            <%: Html.DropDownListFor(x => x.Invoice.CustomerID, Model.Customers)%>
            <%: Html.ValidationMessageFor(x => x.Invoice.CustomerID)%>
        </div>
    <% } %>
    </div>
    <div class="content-right" id="details" style=" clear:both;">
        <div id="workdays">
            <%: Html.DisplayFor(x => x.Workdays) %>
        </div>
        <div id="products">
            <%: Html.DisplayFor(x => x.Products) %>
        </div>
    </div>
</asp:content>