Make sure that the controller has a parameterless public constructor in Unity

Question

I got this problem with the Controller:
An error occurred when trying to create a controller of type '*.WebMvc.Controllers.HomeController'. Make sure that the controller has a parameterless public constructor.

Find the solution for the ApiController, but didn't find anything about normal Controller.

Created new MVC 4 project from scratch.

HomeController.cs:

public class HomeController : Controller
{
    private IAccountingUow _uow;
    public HomeController(IAccountingUow uow)
    {
        _uow = uow;
    }

UnityDependencyResoler.cs:

public class UnityDependencyResolver : IDependencyResolver
{
    private IUnityContainer _container;
    public UnityDependencyResolver(IUnityContainer container)
    {
        _container = container;
        RegisterTypes();
    }
    public object GetService(Type serviceType)
    {
        try
        {
            return _container.Resolve(serviceType);
        }catch
        {
            return null;
        }
    }

    public IEnumerable<object> GetServices(Type serviceType)
    {
        try
        {
            return _container.ResolveAll(serviceType);
        }catch
        {
            return null;
        }
    }

    private void RegisterTypes()
    {
        _container.RegisterType<IAccountingUow, AccountingUow>();

    }
}

Global.asax

    protected void Application_Start()
    {
        //Omitted
        DependencyResolver.SetResolver( new UnityDependencyResolver( new UnityContainer()));

    }

Debugged and found out, that there are even no attempts to resolve IAccountingUow.

What i'm doing wrong? Thinking about it whole day.

Yaroslav Yaroslav · Accepted Answer · 2012-11-13T09:50:54

Found where is the issue. Maybe some one will face the same. The problem is that Unity could not resolve the IAccountingUow, because of hierarchical dependancy on interfaces.

AccountingUow class has two contuctors

    public AccountingUow( IRepositoryProvider repositoryProvider)
    {
        Init(repositoryProvider);
    }
    public AccountingUow()
    {
        Init( new RepositoryProvider(new RepositoryFactories()) );
    }

Dependency Resolver is not smart enought to take the default parametless contructor. It tries to take interface dependant contructor and fails to resolve it, cause there are no rules for resolving it.

I commented out interface dependant constructor and everything worked fine.

I will post later resolver for the first contructor, maybe someone will use it.

Make sure that the controller has a parameterless public constructor in Unity

2 Answers