"；没有为这个对象定义无参数构造函数“；提交带有DropDownList的表单时出错

当我点击下面例子中的提交按钮时，我会收到一条错误消息，如下所示：

没有为此对象定义无参数构造函数。

收到错误消息后，我无法继续使用该应用程序。我试着调试，但没有得到任何有用的信息来帮助解决这个问题。

控制器：

[MvcApplication.SessionExpire]
    [HttpGet]
    public ActionResult Index()
    {
        DataLinqDB db = new DataLinqDB();
        OpgaverPage model = new OpgaverPage();
        var random = new Random();
        var antalopgaver = db.opgavers.Count();
        var number = random.Next(antalopgaver);
        List<opgaver> List = db.opgavers.Skip(number).Take(1).ToList();
        var A = db.opgavers.Skip(number).Take(1).FirstOrDefault();
        model.Overskift = A.overskift;
        model.OpgaveValueList = new SelectList(
                                new List<SelectListItem>
                                {
                                    new SelectListItem { Selected = true, Text = A.svar1, Value = "A"},
                                    new SelectListItem { Selected = false, Text = A.svar2, Value = "B"},
                                    new SelectListItem { Selected = false, Text = A.svar3, Value = "C"},
                                }, "Value", "Text", 1);
        //angiver id til opgaven
        model.HiddenId = A.Id;
        //Fremvis hvornår man har fået point
        //List<pointantal> PointValue = db.pointantals.Where(x => x.omrade == o && x.brugerid == brugerId).OrderByDescending(i => i.Id).Take(20).ToList();
        //model.ListPoint = PointValue.ToList();
        return View(model);
    }
    //error her
    [MvcApplication.SessionExpire]
    [HttpPost]
    public ActionResult index(OpgaverPage opgavervalue)
    {
        if (ModelState.IsValid)
        {
            DataLinqDB db = new DataLinqDB();
            var opgaver = db.opgavers.FirstOrDefault(i => i.Id == opgavervalue.HiddenId);
            if (opgaver != null)
            {
                if (new SelectList(opgavervalue.OpgaveValueList).SelectedValue.ToString() == "A" 
                    || new SelectList(opgavervalue.OpgaveValueList).SelectedValue.ToString() == "B" 
                    || new SelectList(opgavervalue.OpgaveValueList).SelectedValue.ToString() == "C")
                {
                    Value();
                }
                else
                {
                    //error
                    ModelState.AddModelError("", "Desværre dit svar forkert");
                }
            }
            else
            {
                return RedirectToAction("index", opgavervalue);
            }
        }
        return View();
    }

型号：

public class OpgaverPage
{
    public string Overskift
    {
        get; set;
    }
    public int HiddenId
    {
        get; set;
    }
    [Display(Name ="Spørgsmål")]
    public string Svar
    {
        get; set;
    }
    public SelectList OpgaveValueList
    {
        get; set;
    }
    public List<opgaver> ListPoint
    {
        get; set;
    }
}

视图：

@using (Html.BeginForm("index", "spil"))
{
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)
    @Html.HiddenFor(i => i.HiddenId)
    <div class="form-group">
        @Html.LabelFor(x => x.Svar)<br />
        @Html.DropDownListFor(x => x.OpgaveValueList, Model.OpgaveValueList, new
   {
       @class = "form-control"
   })
    </div>

    <button type="submit" class="btn btn-effect-ripple btn-success"><i class="fa fa-check"></i> Tjek mit svar</button>
}

我试图遵循这里的答案，但我无法解决问题：ASP.NET MVC下拉列表From SelectList

是什么导致了这个问题？

public string SelectedOpgaveValue { get; set; }

 @Html.DropDownListFor(x => x.SelectedOpgaveValue, Model.OpgaveValueList, new { @class = "form-control" })

public IEnumerable<SelectListItem> OpgaveValueList { get; set; }
model.OpgaveValueList = new List<SelectListItem>
{
    new SelectListItem { Text = A.svar1, Value = "A"},
    new SelectListItem { Text = A.svar2, Value = "B"},
    new SelectListItem { Text = A.svar3, Value = "C"},
};