Asp.net mvc 4 DropDownList使用viewmodel MVC4返回空值

视图模型：

namespace CFMembers.ViewModels
{
    public class IndexData
    {

        public LicenseHolder LicenseHolders { get; set; }
        public Installation Installations { get; set; }

    }
}

控制器：

public ActionResult Create()
{

        LicenseHolder licenseHolder = new LicenseHolder();



        IndexData ViewData = new IndexData
        {
            LicenseHolders = licenseHolder,

        };

        PopulatePartyTypeDropDownList();
        PopulateLicenseHolderTypeDropDownList();
        return View(ViewData);

    }

    //
    // POST: /Main/Create

    [ActionName("Create"), AcceptVerbs(HttpVerbs.Post)]
    public ActionResult CreateSubmit(IndexData viewModel)
    {


        if (ModelState.IsValid)
        {

            db.LicenseHolder.Add(viewModel.LicenseHolders);
            db.Installation.Add(viewModel.Installations);

            db.SaveChanges();
            return RedirectToAction("Index");
        }


        return View();
    }

Create.cshtml

<div class="editor-label">
    @Html.LabelFor(model => model.LicenseHolders.LicenseHolderTypeID, "License Type")
 </div>
 <div class="editor-field">
    @Html.DropDownList("LicenseHolderTypeID", String.Empty)
    @Html.ValidationMessageFor(model => model.LicenseHolders.LicenseHolderTypeID)               
</div>

---

@在另一个视图中，Html.DropDownList可以正常工作。但是，在具有多个表的viewmodel上不存在这种情况。回发时，LicenseHolderTypeID为0，无论我做什么。我也尝试过dropdownlistfor，但仍然得到0。任何助手都将不胜感激。我想这与viewmodel的传递方式有关，但我被卡住了

我成功了：-在Create.cshtml@Html.DropDownListFor model=>model.LicenseHolders.LicenseHolderTypeID中，选择ListViewBag.LicenseHolderTypeID，licenseholdertypeyes:，选择正确