ViewModel中的ASP.NET MVC SelectList

我在ASP.NET MVC 5中工作(但这很可能也适用于以前的版本).提出这个问题的最佳方式是向您展示代码:

这是视图模型:

public class PersonCreateViewModel
{
    public SelectList cities {get; set;}
    public String Name { get; set; }
    public String Address { get; set; }

}

这是控制器的http Post方法:

[HttpPost]
[ValidateAntiForgeryToken]
public ActionResult Create(PersonCreateViewModel viewmodel)
{

    if (ModelState.IsValid)
    {
        //Add to database here and return

    }

    //return back to view if invalid db save
    return View(person);
}

这是视图:

        @Html.LabelFor(model => model.person.name, new { @class = "control-label col-md-2" })
        

        @Html.EditorFor(model => model.person.name)
        @Html.ValidationMessageFor(model => model.person.name)
    



        @Html.LabelFor(model => model.person.address, new { @class = "control-label col-md-2" })
        

        @Html.EditorFor(model => model.person.address)
        @Html.ValidationMessageFor(model => model.person.address)
    


    @Html.LabelFor(model => model.person.CityID, "CityID", new { @class = "control-label col-md-2" })
    

        @Html.DropDownList("cities")
        @Html.ValidationMessageFor(model => model.person.CityID)
    

当用户单击"提交"时,浏览器中会显示以下错误消息:"没有为此对象定义无参数构造函数."

我认为这与我在ViewModel中有一个SelectList的事实有关.我认为当视图在表单提交时将模型传递回控制器时,它会调用SelectList的构造函数,但是没有SelectList的无参数构造函数.我不知道该怎么办.任何帮助表示赞赏!!