Using Unity with Web Api 2 gives error does not have a default constructor

Question

I have ASP.NET MVC5 web application and i also have Web API in the same application. I am uisng Unity (version 4) for DI. I am configuring the Unity container on APP start as below

        public class MvcApplication : System.Web.HttpApplication
        {
            protected void Application_Start()
            {
                UnityConfiguration.Config();
            }
        }

        public class UnityConfiguration()
        {
         public void Config()
         {
                UnityContainer container = new UnityContainer();
                container.RegisterType<IMyService, Myservice>();
                container.RegisterType<IGenericRepository, GenericRepository>();
                container.RegisterType<DbContext, MyEntities>();            
         }
        }

        public class GenericRepository:IGenericRepository
        {
           private DbContext _dbcontext;
           public GenericRepository(DbContext dbcontext)
           {
               _dbcontext = dbcontext;
           }
        }
        public class MyService:IMyService
        {
           private IGenericRepository _repo;
           publi void MyService(IGenericRepository repository)
           {
              _repo = repository;
           }
        }


        public class MyApiController:ApiController
        {
           provate IMyService _service;
           MyApiController(IMyService myservice)
           {
              _service = myservice;
           }

           public IEnumerable<MyModel> GetData()
           {
             var result = _service.GetData();
             return result.ConvertToMyModel();
           }
        }

However when i call the url like

localhost://lookup/getdata

I get error

Type 'LookupController' does not have a default constructor

How do i solve this issue? Do i need to register each controller i create with Unity or Unity automatically registers all MVC controllers?

Answer 1

I tend to use the Unity.Mvc-package.

You do not need to register the controllers, but you need to register Unity with WebAPI.

   public class UnityConfiguration()
   {
       public IUnityContainer Config()
       {
            IUnityContainer container = new UnityContainer();
            container.RegisterType<IMyService, Myservice>();
            container.RegisterType<IGenericRepository, GenericRepository>();
            container.RegisterType<DbContext, MyEntities>(); 

            // return the container so it can be used for the dependencyresolver.  
            return container;         
       }
    }

    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Your routes...

            // Register Unity with Web API.
            var container = UnityConfiguration.Config();
            config.DependencyResolver = new UnityResolver(container);

            // Maybe some formatters?
        }
    }

You also need a DependencyResolver:

public class UnityResolver : 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();
    }
}

You can also take a look at this similiar question, except for the Owin-part. Unity.WebApi | Make sure that the controller has a parameterless public constructor

Answer 2

I had the same error and in my case the problem was, that i forgot to register a dependency that one of the classes, I had registered for dependency injection, injects in the constructor.

In your example, could it be that you inject something into MyEntities that you forgot to Register?

Answer 3

Install Nuget Package Unit.WebAP instead of Unity.MVC5 Make sure the correct unity package is installed using nuget

I Installed Unity.MVC5 and was facing similar exception "parameterless constructor"

  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>();
        container.RegisterType<ICar, Tesla>();
        GlobalConfiguration.Configuration.DependencyResolver = new UnityDependencyResolver(container);
    }