Using dependency injection with an ApiController when it also needs an empty constructor?

Question

I have an ApiController in an Area of my MVC website, I'm injecting dependencies into it via Unity and my controllers extend the System.Web.Http.ApiController.

I'm using Unity from Microsoft.Practices.Unity.dll, v3.0.0.0.

I can route to the controller with the following in ApiAreaRegistration

context.MapRoute(
    "Api_default",
    "Api/users/{action}/{id}"
);

But I get the following error :

Type 'Project.Areas.Api.Controllers.UsersController' does not have a default constructor

However if I add a default constructor my dependencies don't get resolved.

I'm beginning to feel like I'm missing something structural?

MapRoute isn't related to your Unity problem. Is your controller extending System.Web.Http.ApiController? Are you using the Unity.WebApi package? — Jasen
– Jasen, Commented Aug 27, 2013 at 0:18
@Jasen, Thanks I've added the details to my original question. — Richard Adams
– Richard Adams, Commented Aug 27, 2013 at 10:06
You do realize that there are separate dependency resolver registrations for WebApi, compared to MVC, right? — Erik Funkenbusch
– Erik Funkenbusch, Commented Sep 2, 2013 at 21:54

Jasen · Accepted Answer · 2013-08-27 21:35:10Z

You don't show your controller registration and the error message suggests you have not registered the controller dependencies.

I use the Unity.WebAPI NuGet package to take care of the controller build-up and container lifetime management. If your project also uses MVC controllers the Unity.Mvc3 will handle those controllers. These packages get Unity wired-up for my controllers with very little code.

My Unity bootstrap looks like this

public static class UnityConfig
{
    var container = BuildUnityContainer();

    // MVC controllers
    DependencyResolver.SetResolver(new Unity.Mvc3.UnityDependencyResolver(container));
    // WebAPI controllers
    GlobalConfiguration.Configuration.DependencyResolver = new Unity.WebApi.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<IUsersService, UsersService>();
    ...
    return container;
}

And I don't worry about my controller creation -- It just works.

public class UsersController : ApiController
{
    private IUsersService service;

    public UsersController(IUsersService service)
    {
        this.service = service;
    }

    ...
}

Poul K. Sørensen · Accepted Answer · 2013-09-02 20:16:03Z

2

    GlobalConfiguration.Configuration.DependencyResolver =
        new UnityDependencyResolver(YOUR_UNITY_CONTAINER);

and from http://msdn.microsoft.com/en-us/library/dn178463(v=pandp.30).aspx#sec18 you can find that you should search for 'Unity bootstrapper for ASP.NET WebApi' and you get the UnityDependencyResolver from the namespace: 'Microsoft.Practices.Unity.WebApi'.

Easiest way is just to install the WebApi Bootstrapper and look in the App_Start folder.

answered Sep 2, 2013 at 20:16

Poul K. Sørensen

17.7k24 gold badges141 silver badges296 bronze badges

Collectives™ on Stack Overflow

Using dependency injection with an ApiController when it also needs an empty constructor?

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related