Johann Johann - 3 months ago 48
C# Question

Api Controller has a parameterless public constructor error

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

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...

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