Api Controller has a parameterless public constructor error

Question

I am using Unity to do my DI and I have encountered the following error:-

"An error occurred when trying to create a controller of type 'UploadController'. Make sure that the controller has a parameterless public constructor."

I have the following UnityResolver:-

public class UnityResolver : IDependencyResolver, IDependencyScope, System.Web.Http.Dependencies.IDependencyResolver
{
    protected IUnityContainer container;

    public UnityResolver(IUnityContainer container)
    {
        if (container == null)
        {
            throw new ArgumentNullException("container");
        }
        this.container = container;
    }

    public object GetService(Type serviceType)
    {
        try
        {
            return container.Resolve(serviceType);
        }
        catch (ResolutionFailedException)
        {
            return null;
        }
    }

    public IEnumerable<object> GetServices(Type serviceType)
    {
        try
        {
            return container.ResolveAll(serviceType);
        }
        catch (ResolutionFailedException)
        {
            return new List<object>();
        }
    }

    public IDependencyScope BeginScope()
    {
        var child = container.CreateChildContainer();
        return new UnityResolver(child);
    }

    public void Dispose()
    {
        container.Dispose();
    }
}

}

I have created a UnityConfig as follows:-

public static class UnityConfig
{
    public static void RegisterComponents()
    {
        var container = new UnityContainer();

        // register all your components with the container here
        // it is NOT necessary to register your controllers

        // e.g. container.RegisterType<ITestService, TestService>();

        BuildUnityContainer();
        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }

    private static IUnityContainer BuildUnityContainer()
    {
        var container = new UnityContainer();

        // register all your components with the container here
        // you don't need to register controllers
        container.RegisterType<IFileHelpers, FileHelpers>();
        container.RegisterType<IDatabaseHelper, DatabaseHelper>();
        container.RegisterType<IPlayersHelpers, PlayersHelpers>();
        container.RegisterType<IBaseRepository, BaseRepository>();
        container.RegisterType<IAttribsRepository, AttribsRepository>();
        container.RegisterType<IPlayerRepository, PlayerRepository>();
        container.RegisterType<IFileRepository, FileRepository>();
        container.RegisterType<IPlayerAttribsRepository, PlayerAttribsRepository>();

        container.RegisterType<FMContext>();
        container.RegisterType<UserManager<ApplicationUser>>(new HierarchicalLifetimeManager());
        container.RegisterType<IUserStore<ApplicationUser>, UserStore<ApplicationUser>>(new HierarchicalLifetimeManager());

        return container;
    }
}

}

Im initializing everyting in the WebApiConfig.cs

    public static void Register(HttpConfiguration config)
    {
        // Web API configuration and services
        // Configure Web API to use only bearer token authentication.
        config.SuppressDefaultHostAuthentication();
        config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));

        // Web API configuration and services
        var container = new UnityContainer();
        UnityConfig.RegisterComponents();
        config.DependencyResolver = new UnityResolver(container);

        config.EnableCors();

        // Web API routes
        config.MapHttpAttributeRoutes();

        config.Routes.MapHttpRoute(
            name: "DefaultApi",
            routeTemplate: "api/{controller}/{id}",
            defaults: new { id = RouteParameter.Optional }
        );
    }
}

And this is my UploadController class:-

    public class UploadController : ApiController
{
    private readonly IFileHelpers _fileHelpers;
    private readonly IDatabaseHelper _databaseHelper;
    private readonly IPlayersHelpers _playersHelpers;

    public UploadController(IFileHelpers fileHelpers, IDatabaseHelper databaseHelper, IPlayersHelpers playersHelpers)
    {
        _fileHelpers = fileHelpers;
        _databaseHelper = databaseHelper;
        _playersHelpers = playersHelpers;
    }

    public async Task<HttpResponseMessage> Post()
    {........................}

Can you please help me in determining what am I doing wrong. Do I need to declare something else for this to work?

Thanks for your help and time

Answer 1

In your Register method, you have the following code:

// ...
// Web API configuration and services
var container = new UnityContainer();
UnityConfig.RegisterComponents();
config.DependencyResolver = new UnityResolver(container);

However, there is nothing registered to that container. There is a separate container (with registrations) being created in your static UnityConfig class, but that container is not being passed to the UnityResolver object...