NullReferenceException on DropDownListFor after [HttpPost]

Question

In my application I'am populating a dropdownlist from database using ADO Entity Framework, after this when i try to submit the form the value of the dropdown list it is giving Null reference exception.

Error Code (in INDEX.ASPX)

<%: Html.DropDownListFor(model => model.race, Model.Races, "--Select--")%>  <--error
<%: Html.ValidationMessageFor(model => model.race)%>

CONTROLLER (in NewPersonController)

public ActionResult Index()
        {
            Person person= new Person();
            return View(new PersonFormViewModel(person));   
        }


[HttpPost]
public ActionResult Index(Person person)
        {
            if (ModelState.IsValid) //Also not enter the race parameter
            {
                personRepo.Add(person);
                personRepo.Save();
            }
            return View();  // When return the view I get the error
        }

MODEL (in PersonFormViewModel)

public class PersonFormViewModel
    {


        public Person Person        {
            get;
            private set;
        }

        public SelectList Races
        {
            get;
            private set;
        }

        public string race
        {
            get { return Person.race; }
            set { Person.race = value; }
        }


        public PersonFormViewModel(Person person)
        {

            Person = person;
            RaceRepository repository = new RaceRepository();

            IList<Race> racesList= repository.FindRaces().ToList();
            IEnumerable<SelectListItem> selectList =
                from c in racesList
                select new SelectListItem
                {
                    Text = c.race,
                    Value = c.id.ToString()
                };

            Races = new SelectList(selectList, "Value", "Text");   
        }

    }

IN VALIDATION MODEL

[MetadataType(typeof(Person_Validation))]
public partial class Person    {

}

    public class Person_Validation
    {

        [Required(ErrorMessage = "Required race")]
        public string race
        {
            get;
            set;
        }
    }

Can you help me please? Thank you.

possible duplicate of What is a NullReferenceException in .NET? — John Saunders
– John Saunders, Commented Jun 1, 2011 at 14:37

DanielB · Accepted Answer · 2011-06-01 14:38:42Z

1

In the POST method you have to give the same type of model to the view.

        [HttpPost]
        public ActionResult Index(Person person)
        {
            if (ModelState.IsValid)
            {
                personRepo.Add(person);
                personRepo.Save();
            }
            return View(new PersonFormViewModel(person));
        }

answered Jun 1, 2011 at 14:38

DanielB

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2 Comments

Xenetrix Over a year ago

Ok Thank you, I replace the return in [HttPost] by return View(new PersonFormViewModel(person)), but the variable raze is never catched. the race variable still null and never detected by Person_Validation.

Xenetrix Over a year ago

Thanks to Eduardo Campañó and DanielB. First I need to replace in [HttPost]: return View() by return View(new PersonFormViewModel(person)) and the problem with never detected by Person_Validation just I need to replace: <%: Html.DropDownListFor(model => model.race, Model.Races, "--Select--")%> by <%: Html.DropDownListFor(model => model.Person.race, Model.Races, "--Select--")%> Thank you soo much!!!

Eduardo Campañó · Accepted Answer · 2011-06-01 15:08:38Z

0

You're not passing the ViewModel in the post action.

[HttpPost]
public ActionResult Index(Person person)
{
    if (ModelState.IsValid) //Also not enter the race parameter
    {
        personRepo.Add(person);
        personRepo.Save();
    }
    return View(new PersonFormViewModel(person));
}

Or maybe

[HttpPost]
public ActionResult Index(Person person)
{
    if (ModelState.IsValid) //Also not enter the race parameter
    {
        personRepo.Add(person);
        personRepo.Save();
    }
    return RedirectToAction("Index");
}

edited Jun 1, 2011 at 15:08

answered Jun 1, 2011 at 14:38

Eduardo Campañó

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2 Comments

Xenetrix Over a year ago

Ok thank you, I replace the return in [HttPost] by return View(new PersonFormViewModel(person)), but the the variable raze is never catched. the race variable still null and never detected by Person_Validation.

Xenetrix Over a year ago

Thanks to Eduardo Campañó and DanielB. First I need to replace in [HttPost]: return View() by return View(new PersonFormViewModel(person)) and the problem with never detected by Person_Validation just I need to replace: <%: Html.DropDownListFor(model => model.race, Model.Races, "--Select--")%> by <%: Html.DropDownListFor(model => model.Person.race, Model.Races, "--Select--")%> Thank you soo much!!!

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