mvc 4 Model is null

Question

i'm using razor's listboxfor for the first time, but my Model is always null. after reading similar posts and tryouts it still won't work.

Person.cshtml

@model SampleApp.Web.ViewModel.PersonViewModel

@{
     ViewBag.Title = "Welcome";
}

<article>
   <p>
      Welcome to example page. 
   </p>

   <p>
     <div class="container">

 //Post data works as expected, controllers create method write to db successfully 
 @using (Html.BeginForm("Create", "Person", FormMethod.Post, new { enctype =   "multipart/form-data" }))
 {
    @Html.AntiForgeryToken()
    @Html.ValidationSummary(true)

    <fieldset>
        <legend>Personen</legend>

        <div class="editor-label">
           @* @Html.LabelFor(model => model.Name)
        </div>
        <div class="editor-field">
            @Html.EditorFor(model => model.Age)
            @Html.ValidationMessageFor(model => model.Age)
        </div>

        <div class="editor-label">
            @Html.LabelFor(model => model.Surrname)
        </div>
</fielset>
 </div>

 <p>
    <input type="submit" value="Create" />
 </p>
}

//binding to Model fails, Model is null. Not be able to debug anything in    controller action, it stops when "loading" the page
@using (Html.BeginForm("GetListBoxData", "Person"))
{
   @Html.AntiForgeryToken()
   @Html.ValidationSummary(true)
   @Html.ListBoxFor(model => model.ListboxData, Model.ListboxData);
}

</div>

PersonController.cs

[AcceptVerbs(HttpVerbs.Get)]
    [ValidateAntiForgeryToken]
    public ActionResult GetListBoxData()
    {
        var data = new List<PersonViewModel>();
        data.Add(new PersonViewModel{Name = "Test", Surrname="testsurrname", Age=30});

        var viewModel = new PersonViewModel()
        {
            ListboxData = data.AsEnumerable().Select(s=> new SelectListItem{Value=s.Name ,Text = s.Surrname}),
        };

        return View(viewModel);
    }

    [AcceptVerbs(HttpVerbs.Post)]
    [ValidateAntiForgeryToken]
    public ActionResult GetListBoxData(PersonViewModel persondata)
    {
        //TODO: handle values from View
        return View(this);
    }

    [ValidateAntiForgeryToken]
    [AcceptVerbs(HttpVerbs.Post)]
    public ActionResult Create([Bind(Include = "Name, Surrname, Age")]  PersonViewModel persondata)
    {
        try
        {
            PersonService personDataProvider = new PersonService();
            personDataProvider.SavePerson(persondata);

            return new RedirectResult("SomewhereToGo");
        }
        catch (DataException ex)
        {
            //TODO: Log
        }

        return View(this);
    }

PersonViewModel

public class PersonViewModel
{
    public int PersonId{ get; set; }
    public int Age { get; set; }
    public string Name { get; set; }
    public string Surrname { get; set; }
    public IEnumerable<SelectListItem> ListboxData { get; set; }
}

writing values from editFor to db works as expected without code for listboxfor. after adding it to my html it should be filled from db on page loading, but I get a ReferenceNotSet Exception on page loading. Model.ListboxData is null, before GetListBoxData action is called.

Thanks a lot for your help!

Solution

1. Your form should submit the data via POST, not GET. And, you don't need to use enctype = "multipart/form-data", unless you want to upload files through your from.
2. You need two Index Actions in your Controller, one is for sending the data from your Controller to the View, and the other one is for getting the data back from the View, when the form is submitted (POST) to the server.
3. The first argument you pass to your ListBox (the expression) refers to the Property in your Model that the selected item from your ListBox will be stored in, which in this case is PersonId.

So, your View should look like this:

@model MVCApplication.Web.ViewModel.PersonViewModel 

@using (Html.BeginForm("Index", "Person"))
{
    @Html.ListBoxFor(model => model.PersonId, Model.ListBoxData)

    <input type="submit" value="Save" />
} 

Then, in your Controller, you'll have two Actions like this:

public ActionResult Index()
{
    var viewModel = new PersonViewModel()
    {
        ListboxData = data.Select(s => new SelectListItem { Value = s.PersonId.ToString(), Text = s.PersonId.ToString() }).AsEnumerable();
    };

    return View(viewModel);
}

[HttpPost]
public ActionResult Index(PersonViewModel viewModel)
{
  // code to save the data in the database or whatever you want to do with the data coming from the View
}

By the way, in your ViewModel, you don't have to define your ListBoxData property like that, just do this:

public class PersonViewModel
{
    public int PersonId{ get; set; }
    public IEnumerable<SelectListItem> ListBoxData { get; set; }
}