C# – Cannot Inject Dependencies into ASP.NET Web API Controller using Unity

asp.net-web-apicnetunity-container

Has anyone had any success running using an IoC container to inject dependencies into ASP.NET WebAPI controllers? I cannot seem to get it to work.

This is what I'm doing now.

In my global.ascx.cs:

    public static void RegisterRoutes(RouteCollection routes)
    {
            // code intentionally omitted 
    }

    protected void Application_Start()
    {
        AreaRegistration.RegisterAllAreas();

        RegisterGlobalFilters(GlobalFilters.Filters);
        RegisterRoutes(RouteTable.Routes);

        IUnityContainer container = BuildUnityContainer();

        System.Web.Http.GlobalConfiguration.Configuration.ServiceResolver.SetResolver(
            t =>
            {
                try
                {
                    return container.Resolve(t);
                }
                catch (ResolutionFailedException)
                {
                    return null;
                }
            },
            t =>
            {
                try
                {
                    return container.ResolveAll(t);
                }
                catch (ResolutionFailedException)
                {
                    return new System.Collections.Generic.List<object>();
                }
            });

        System.Web.Mvc.ControllerBuilder.Current.SetControllerFactory(new UnityControllerFactory(container)); 

        BundleTable.Bundles.RegisterTemplateBundles();
    }

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

        return container;
    }

My controller factory:

public class UnityControllerFactory : DefaultControllerFactory
            {
                private IUnityContainer _container;

                public UnityControllerFactory(IUnityContainer container)
                {
                    _container = container;
                }

                public override IController CreateController(System.Web.Routing.RequestContext requestContext,
                                                    string controllerName)
                {
                    Type controllerType = base.GetControllerType(requestContext, controllerName);

                    return (IController)_container.Resolve(controllerType);
                }
            }

It never seems to look in my unity file to resolve dependencies, and I get an error like:

An error occurred when trying to create a controller of type
'PersonalShopper.Services.WebApi.Controllers.ShoppingListController'.
Make sure that the controller has a parameterless public constructor.

at
System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpControllerContext
controllerContext, Type controllerType)
at System.Web.Http.Dispatcher.DefaultHttpControllerFactory.CreateInstance(HttpControllerContext
controllerContext, HttpControllerDescriptor controllerDescriptor)
at System.Web.Http.Dispatcher.DefaultHttpControllerFactory.CreateController(HttpControllerContext
controllerContext, String controllerName)
at System.Web.Http.Dispatcher.HttpControllerDispatcher.SendAsyncInternal(HttpRequestMessage
request, CancellationToken cancellationToken)
at System.Web.Http.Dispatcher.HttpControllerDispatcher.SendAsync(HttpRequestMessage
request, CancellationToken cancellationToken)

Controller looks like:

public class ShoppingListController : System.Web.Http.ApiController
    {
        private Repositories.IProductListRepository _ProductListRepository;


        public ShoppingListController(Repositories.IUserRepository userRepository,
            Repositories.IProductListRepository productListRepository)
        {
            _ProductListRepository = productListRepository;
        }
}

My unity file looks like:

<unity xmlns="http://schemas.microsoft.com/practices/2010/unity">
  <container>
    <register type="PersonalShopper.Repositories.IProductListRepository, PersonalShopper.Repositories" mapTo="PersonalShopper.Implementations.MongoRepositories.ProductListRepository, PersonalShopper.Implementations" />
  </container>
</unity>

Note that I don't have a registration for the controller itself because in previous versions of mvc the controller factory would figure out that the dependencies needed to be resolved.

It seems like my controller factory is never being called.

Best Answer

Figured it out.

For ApiControllers, MVC 4 uses a System.Web.Http.Dispatcher.IHttpControllerFactory and System.Web.Http.Dispatcher.IHttpControllerActivator to create the controllers. If there is no static method to register what the implementation of these they are; when they are resolved, the mvc framework looks for the implementations in the dependency resolver, and if they are not found, uses the default implementations.

I got unity resolution of controller dependencies working by doing the following:

Created a UnityHttpControllerActivator:

public class UnityHttpControllerActivator : IHttpControllerActivator
{
    private IUnityContainer _container;

    public UnityHttpControllerActivator(IUnityContainer container)
    {
        _container = container;
    }

    public IHttpController Create(HttpControllerContext controllerContext, Type controllerType)
    {
        return (IHttpController)_container.Resolve(controllerType);
    }
}

Registered that controller activator as the implementation in the unity container itself:

protected void Application_Start()
{
    // code intentionally omitted

    IUnityContainer container = BuildUnityContainer();
    container.RegisterInstance<IHttpControllerActivator>(new UnityHttpControllerActivator(container));

    ServiceResolver.SetResolver(t =>
       {
         // rest of code is the same as in question above, and is omitted.
       });
}
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