Question

I have the following viewModel:

namespace Flashcard.Models
{
    public class CreateCardViewModel
    {
        [HiddenInput(DisplayValue = false)]
        public int SetId { get; set; }

        [Required]
        public ICollection<Side> Sides { get; set; }

    }
}

I use this ViewModel against the Card Controller:

public class CardController : Controller
    {
        //
        // GET: /Card/

        public ActionResult Create(int setId)
        {
            var model = new CreateCardViewModel();

            var side = new Side() {Content = "Blank Side"};


            model.SetId = setId;
            model.Sides.Add(side);
            return View(model);
        }

    }

However when I call the Create action, I get a nullReferenceException because model.Sides is null, which does not seem to be the same as empty. I believe I created an empty ICollection Sides in the ViewModel – why is it null in the controller?

For some context – a Card can have one or several Sides. I’m trying to always add a Side whenever a Card is created.

Answer 1

you need to initiate a Collection and assign it to the property of your object as follows:

public class CardController : Controller
{
    //
    // GET: /Card/

    public ActionResult Create(int setId)
    {
        var model = new CreateCardViewModel();

        var side = new Side() {Content = "Blank Side"};


        model.SetId = setId;


        model.Sides = new List<Side>();

        model.Sides.Add(side);
        return View(model);
    }

}

Your collection is null. make one and assign to your prop.