No parameterless constructor defined for this object. in ASP.NET MVC Controller

Question

I am sure this is quite straightforward but I am a bit stuck here. The routing defined for my app is just the default. I have the following controller defined.

namespace Baynes.Wedding.Web.Controllers
{
    public class AdminController : Controller
    {
        private readonly IAuthProvider _authProvider;
        private readonly IDocumentRepository _documentRepository;

        public AdminController(IAuthProvider authProvider, IDocumentRepository documentRepository)
        {
            _authProvider = authProvider;
            _documentRepository = documentRepository;
        }

        public ViewResult EditDocument(int id)
        {
            var document = _documentRepository.Select(id);

            return View(new DocumentEditViewModel(document));
        }

        [HttpPost]
        public ActionResult EditDocument(DocumentEditViewModel model)
        {
            if (ModelState.IsValid)
            {
                _documentRepository.Update(model.ToDocument());
                return RedirectToAction("ListDocuments");
            }

            return View();
        }
    }
}

When I navigate to /Admin/EditDocument/1/ then the first action executes exactly as expected, rendering the following view:-

<h2>@ViewBag.Title</h2>
@using (Html.BeginForm("EditDocument", "Admin", FormMethod.Post)) {
    @Html.ValidationSummary(true)
    @Html.HiddenFor(m => Model.Id)
    <div>
        @Html.LabelFor(m => Model.Title)
    </div>
    <div>
        @Html.TextBoxFor(m => Model.Title)
    </div>
    <div>
        @Html.LabelFor(m => Model.Body)
    </div>
    <div>
        @Html.TextAreaFor(m => Model.Body)
    </div>
    <div>
        @Html.LabelFor(m => Model.Url)
    </div>
    <div>
        @Html.TextBoxFor(m => Model.Url)
    </div>

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

On submitting this I get an error:-

No parameterless constructor defined for this object. Other questions seemingly related questions MVC: No parameterless constructor defined for this object suggest that it is a to do with the IoC container not being set up properly, but surely the fact that the first action executes without a problem means that isn't the problem here?

Any help would be greatly appreciated.

Regards.

Simon

can you please provide code for DocumentViewModel

Parv Sharma
– Parv Sharma

2013-01-17 07:47:35 +00:00
Commented Jan 17, 2013 at 7:47 — Parv Sharma
– Parv Sharma, Commented Jan 17, 2013 at 7:47

Mediator · Accepted Answer · 2013-01-17 07:47:29Z

15

add to class DocumentEditViewModel default constructor

public DocumentEditViewModel (){}

answered Jan 17, 2013 at 7:47

Mediator

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4 Comments

levininja Over a year ago

WHY is this necessary? In my mind, controllers should have default constructors created by the system just like most classes.

Mediator Over a year ago

@levininja JTMon answered on your question

levininja Over a year ago

@Mediator my question is: what is the thinking behind designing MVC framework to not assume a default constructor for controller classes, the way .NET does with ALL classes by default. Normally the compiler assumes an empty constructor if none is specified. NOT doing that for controller classes specifically seems ridiculous to me.

Mediator Over a year ago

@levininja, DefaultModelBinder use System.Activator.CreateInstance(Type type). The documentation told us "Creates an instance of the specified type using that type's default constructor."

JTMon · Accepted Answer · 2013-01-17 07:51:22Z

5

The MVC framework is trying to create an instance of the DocumentViewModel class but it can't find a publicly accessible default constructor (that does not take any arguments). You can either define such a default constructor like @simplyDenis suggested or define a cusotm ModelBinder that can create the instance using your custom constructor.

answered Jan 17, 2013 at 7:51

JTMon

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Comments

chrisn · Accepted Answer · 2013-01-17 07:50:20Z

1

Does DocumentEditViewModel have a parameterless constructor? I believe this is needed for modelbinding on your post view.

answered Jan 17, 2013 at 7:50

chrisn

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Comments

Vitaliy Markitanov · Accepted Answer · 2015-09-01 20:05:50Z

1

Most likely you have dependency injections mechanism. But MVC requires "special" way to register container. Look at this link Adding Unity to Your Web Applications, patterns and practices

answered Sep 1, 2015 at 20:05

Vitaliy Markitanov

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Comments

Jess · Accepted Answer · 2017-03-17 20:58:03Z

0

I had a slightly different problem. One of my Model classes was abstract.

answered Mar 17, 2017 at 20:58

Jess

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Comments

Jamaxack · Accepted Answer · 2017-09-14 10:46:28Z

0

If DocumentEditViewModel constructor's accessibility level is protected you will get also the same error.

answered Sep 14, 2017 at 10:46

Jamaxack

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