Я не могу заставить работать мои выпадающие списки "Месяц, День, Год" из моей ASP.NET MVC3 ViewModel

Question

Я перешел на MVC 3 из Webforms, и у меня возникли проблемы с обучением.Я создал ViewModel, который должен заполнить 3 отдельных списка выбора значениями Месяц, День, Год в моем _Header.Я думаю, что у меня есть проблема со структурой.Конечным результатом является то, что я вызываю необработанное исключение в службе www на моем компьютере, и Visual Studio выскакивает и хочет, чтобы я его отладил.Любая помощь будет с благодарностью!

Вот мой код.

DateSearchViewModel.cs

namespace DH.ViewModels
{
    public class DateSearchViewModel
    {
        //MONTH DROPDOWN LIST
        public class MonthViewModel
        {
           public int ID { set; get; }
           public string Month { set; get; }
        }       

        private List<MonthViewModel> _months;
        public List<MonthViewModel> Months
        {
            get
            {
                if (_months == null)
                {
                    _months = new List<MonthViewModel>();
                    _months.Add(new MonthViewModel { ID = 1, Month = "Jan" });
                    _months.Add(new MonthViewModel { ID = 2, Month = "Feb" });
                    _months.Add(new MonthViewModel { ID = 3, Month = "Mar" });
                    _months.Add(new MonthViewModel { ID = 4, Month = "Apr" });
                    _months.Add(new MonthViewModel { ID = 5, Month = "May" });
                    _months.Add(new MonthViewModel { ID = 6, Month = "Jun" });
                    _months.Add(new MonthViewModel { ID = 7, Month = "Jul" });
                    _months.Add(new MonthViewModel { ID = 8, Month = "Aug" });
                    _months.Add(new MonthViewModel { ID = 9, Month = "Sep" });
                    _months.Add(new MonthViewModel { ID = 10, Month = "Oct" });
                    _months.Add(new MonthViewModel { ID = 11, Month = "Nov" });
                    _months.Add(new MonthViewModel { ID = 12, Month = "Dec" });
                }
                return _months;
            }
        }
        public int SelectedMonthID { set; get; }


        //DAY DROPDOWN LIST
        public class DayViewModel
        {
            public int ID { set; get; }
            public string Day { set; get; }
        }
        private List<DayViewModel> _days;
        public List<DayViewModel> Days
        {
            get
            {
                if (_days == null)
                {
                    _days = new List<DayViewModel>();
                    _days.Add(new DayViewModel { ID = 1, Day = "1" });
                    _days.Add(new DayViewModel { ID = 2, Day = "2" });
                    _days.Add(new DayViewModel { ID = 3, Day = "3" });
                    _days.Add(new DayViewModel { ID = 4, Day = "4" });
                    _days.Add(new DayViewModel { ID = 5, Day = "5" });
                    _days.Add(new DayViewModel { ID = 6, Day = "6" });
                    _days.Add(new DayViewModel { ID = 7, Day = "7" });
                    _days.Add(new DayViewModel { ID = 8, Day = "8" });
                    _days.Add(new DayViewModel { ID = 9, Day = "9" });
                    _days.Add(new DayViewModel { ID = 10, Day = "10" });
                    _days.Add(new DayViewModel { ID = 11, Day = "11" });
                    _days.Add(new DayViewModel { ID = 12, Day = "12" });
                    _days.Add(new DayViewModel { ID = 1, Day = "13" });
                    _days.Add(new DayViewModel { ID = 2, Day = "14" });
                    _days.Add(new DayViewModel { ID = 3, Day = "15" });
                    _days.Add(new DayViewModel { ID = 4, Day = "16" });
                    _days.Add(new DayViewModel { ID = 5, Day = "17" });
                    _days.Add(new DayViewModel { ID = 6, Day = "18" });
                    _days.Add(new DayViewModel { ID = 7, Day = "19" });
                    _days.Add(new DayViewModel { ID = 8, Day = "20" });
                    _days.Add(new DayViewModel { ID = 8, Day = "21" });
                    _days.Add(new DayViewModel { ID = 8, Day = "22" });
                    _days.Add(new DayViewModel { ID = 8, Day = "23" });
                    _days.Add(new DayViewModel { ID = 8, Day = "24" });
                    _days.Add(new DayViewModel { ID = 8, Day = "25" });
                    _days.Add(new DayViewModel { ID = 8, Day = "26" });
                    _days.Add(new DayViewModel { ID = 8, Day = "27" });
                    _days.Add(new DayViewModel { ID = 8, Day = "28" });
                    _days.Add(new DayViewModel { ID = 8, Day = "29" });
                    _days.Add(new DayViewModel { ID = 8, Day = "30" });
                    _days.Add(new DayViewModel { ID = 8, Day = "31" });
                }
                return _days;
            }
        }
        public int SelectedDayID { set; get; }


        //YEAR DROPDOWN LIST
        public class YearViewModel
        {
            public int ID { set; get; }
            public string Year { set; get; }
        }
        private List<YearViewModel> _years;
        public List<YearViewModel> Years
        {
            get
            {
                if (_years == null)
                {
                    _years = new List<YearViewModel>();
                    _years.Add(new YearViewModel { ID = 1, Year = "2009" });
                    _years.Add(new YearViewModel { ID = 2, Year = "2010" });
                    _years.Add(new YearViewModel { ID = 3, Year = "2011" });
                    _years.Add(new YearViewModel { ID = 4, Year = "2012" });
                }
                return _years;
            }
        }    
        public int SelectedYearID { set; get; }
    }
}

CommonController.cs:

[ChildActionOnly]
public ActionResult _Header()
{
    DateSearchViewModel DateVM = new DateSearchViewModel();
    return View(DateVM);
}

_Header.cshtml:

@model DH.ViewModels.DateSearchViewModel

@Html.DropDownListFor(x => x.SelectedMonthID, new SelectList(Model.Months, "ID", "Month"), "--Select--")
@Html.DropDownListFor(x => x.SelectedDayID, new SelectList(Model.Days, "ID", "Day"), "--Select--")
@Html.DropDownListFor(x => x.SelectedYearID, new SelectList(Model.Years, "ID", "Year"), "--Select--")

_Layout.cshtml:

@{Html.RenderAction("_Header", "Common");}

Answer 1

Я чувствую, что ваша модель слишком усложнена ... наличие модели представления в течение месяца и года кажется мне излишним. Я бы просто реализовал их как свойства. Вот как бы я это сделал:

Модель:

public class DateSearchViewModel {
  public int Day { get; set; }
  public int Month { get; set; }
  public int Year { get; set; }
}

Контроллер:

public ActionResult _Header() {
  DateSearchViewModel DateVM = new DateSearchViewModel();
  return View(DateVM);
}
public ActionResult _Header( DateSearchViewModel vm ) {
  if( ModelState.IsValid ) {
    // save vm to database, etc.
  }
  return View(vm);
}

А вид:

@{
  var days = new List<SelectListItem>();
  for( var i = 1; i <= 31; i++ ) {
    days.Add( new SelectListItem { Text = i.ToString(), Value = i.ToString(), Selected = Model.Day == i } );
  }
  var months = new List<SelectListItem> {
    new SelectListItem {Text = "Jan", Value = "1", Selected = Model.Month == 1},
    new SelectListItem {Text = "Feb", Value = "2", Selected = Model.Month == 2},
    new SelectListItem {Text = "Mar", Value = "3", Selected = Model.Month == 3},
    new SelectListItem {Text = "Apr", Value = "4", Selected = Model.Month == 4},
    new SelectListItem {Text = "May", Value = "5", Selected = Model.Month == 5},
    new SelectListItem {Text = "Jun", Value = "6", Selected = Model.Month == 6},
    new SelectListItem {Text = "Jul", Value = "7", Selected = Model.Month == 7},
    new SelectListItem {Text = "Aug", Value = "8", Selected = Model.Month == 8},
    new SelectListItem {Text = "Sep", Value = "9", Selected = Model.Month == 9},
    new SelectListItem {Text = "Oct", Value = "10", Selected = Model.Month == 10},
    new SelectListItem {Text = "Nov", Value = "11", Selected = Model.Month == 11},
    new SelectListItem {Text = "Dec", Value = "12", Selected = Model.Month == 12},
  };
  var years = new List<SelectListItem>();
  for( var i = 2009; i <= 2012; i++ ) {
    years.Add( new SelectListItem { Text = i.ToString(), Value = i.ToString(), Selected = Model.Year == i } );
  }
}
@using( Html.BeginForm() ) {
  @Html.DropDownListFor( x => x.Month, months )
  @Html.DropDownListFor( x => x.Day, days )
  @Html.DropDownListFor( x => x.Year, years )
  <input type="submit" />
}