NullReferenceException in use DropDownListFor in ASP.NET MVC 5

Question

I can't find the answer why I'm getting NullReferenceException when I'm trying to use DropDownListFor() like this:

View:

<div class="form-group">
    @Html.LabelFor(m => m.Category, new { @class = "col-md-2 control-label" })
    <div class="col-md-10">
        @Html.DropDownListFor(
            m => m.Category,
            new SelectList(Model.CategoryOptionsList, "CategoryOptionId", "Value", Model.CategoryOptionsList.First().CategoryOptionId),
            new { @class = "form-control" }
            )
    </div>
</div>

ViewModel:

public class CategoryOption 
{
    public int CategoryOptionId { get; set; }
    public string Value { get; set; }
}

public IEnumerable<CategoryOption> CategoryOptionsList = new List<CategoryOption> 
{
    new CategoryOption { CategoryOptionId = 0, Value="Rock" },
    new CategoryOption { CategoryOptionId = 1, Value="Jazz" },
    new CategoryOption { CategoryOptionId = 2, Value="Pop" },
    new CategoryOption { CategoryOptionId = 3, Value="Metal" },
    new CategoryOption { CategoryOptionId = 4, Value="Folk" }
};

[Required]
[Display(Name = "Kategoria")]
public string Category { get; set; }

did you set your ViewModel ? and did you pass your model to the View when you returning it from controller? — Selman Genç
– Selman Genç, Commented Feb 12, 2014 at 22:03
Selman22 - yes, i've passed like this: '@model IdentityTesting.Models.RegisterViewModel' SimonWhitehead '@Html.DropDownListFor( m => m.Category, //this line throws error. new SelectList(Model.CategoryOptionsList, "CategoryOptionId", "Value", Model.CategoryOptionsList.First().CategoryOptionId), new { @class = "form-control" } )' — magos
– magos, Commented Feb 12, 2014 at 22:16
possible duplicate of What is a NullReferenceException and how do I fix it? — John Saunders
– John Saunders, Commented Feb 12, 2014 at 23:01
@magos: @model IdentityTesting.Models.RegisterViewModel only tells the view what the expected type of the model is. It doesn't actually make an object and pass it to the view. That's what your controller is supposed to do. — Flater
– Flater, Commented Apr 23, 2014 at 11:07

abatishchev · Accepted Answer · 2014-02-12 22:21:45Z

18

I think you forgot to pass your ViewModel object to your view, see below:

public ActionResult YourAction()
{
    return View(new YourViewModel());
}

edited Feb 12, 2014 at 22:21

abatishchev

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answered Feb 12, 2014 at 22:09

Lin

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