IoC: Castle Windsor and WebAPI

Question

I have an MVC4 site using Castle Windsor that I want to add some WebAPI calls to, so I start digging around a little bit on the interwebs.

Now I don't know the ins and outs of IoC; I followed a tutorial for how to set up Castle Windsor on my project, injecting the IUnitOfWorkFactory and the IApplicationService as public properties in a base controller, and a few other interfaces as needed in the controller constructors. It works swimmingly, so I've never had to do more with it.

Everywhere that I'm reading up on WebAPI, I'm told DI will not work so well using Castle Windsor, talking about problems with the IDependencyResolver and IDependencyScope. There are several workarounds and implementations of how to get around this problem, but what is not clear to me is what exactly the problem is. Code snippets are included, but the assumption is you know what class they belong to, and how they are invoked, which unfortunately I do not. Additionally, all the examples I've seen online refer to an exclusive WebAPI project, and not an MVC4 project with a couple ApiControllers judiciously tossed in. I don't know how, or if, this affects anything.

Why won't what I have working with my standard controllers not work with an API controller? What kind of code acrobatics need to do to get WebAPI calls and standard web calls to work in the same application?

Answer 1

Existing Castle Windsor MVC configuration

Assuming you have MVC and Castle Windsor setup similarly to the Castle Windsor MVC tutorial, adding IoC to get Web API controllers to utilize dependency injection is very simple with Mark Seemann's post (note that he explains why not to use IDependencyResolver).

From the Castle Windsor tutorial you should have something like this in Global.asax.cs.

    private static IWindsorContainer container;

    protected void Application_Start()
    {
        //... MVC / Web API routing etc.
        BootStrapper bs = new BootStrapper();
        container = bs.ConfigureCastleWindsorMVC();
    }

BootStrapper.ConfigureCastleWindsorMVC() snip

        IWindsorContainer container = new WindsorContainer()
            .Install(
                new LoggerInstaller()
                //...,
                , new ControllersInstaller()
            );

        var controllerFactory = new WindsorControllerFactory(container.Kernel);
        ControllerBuilder.Current.SetControllerFactory(controllerFactory);
        return container;

Required changes

From Mark Seemann's post you need to get into Web API's entry point (Composition Root) through the IHttpControllerActivator. Here's his adapter implementation which you need.

public class WindsorCompositionRoot : IHttpControllerActivator
{
    private readonly IWindsorContainer container;

    public WindsorCompositionRoot(IWindsorContainer container)
    {
        this.container = container;
    }

    public IHttpController Create(HttpRequestMessage request,
        HttpControllerDescriptor controllerDescriptor, Type controllerType)
    {
        var controller =
            (IHttpController)this.container.Resolve(controllerType);

        request.RegisterForDispose(
            new Release(() => this.container.Release(controller)));

        return controller;
    }

    private class Release : IDisposable
    {
        private readonly Action release;

        public Release(Action release) { this.release = release; }

        public void Dispose()
        {
            this.release();
        }
    }
}

With the IHttpControllerActivator adapter and the MVC Castle Windsor container implementation, you just need to configure it in the Global.asax.cs (or in BootStrapper if you used that). It has to be after the MVC initialization since the MVC initialization has all of the installers.

    private static IWindsorContainer container;

    protected void Application_Start()
    {
        // MVC / Web API routing etc.
        BootStrapper bs = new BootStrapper();
        container = bs.ConfigureCastleWindsorMVC();
        // Web API Castle Windsor ++ ADD THIS ++
        GlobalConfiguration.Configuration.Services.Replace(
            typeof(IHttpControllerActivator),
            new WindsorCompositionRoot(container));
    }

Final Result:

The Web API controllers can use your injected dependencies the same as your MVC controllers.

public class TestController : ApiController
{
    private readonly ITestService TestService;

    public TestController(ITestService testService)
    {
        this.TestService = testService;
    }

    // GET api/<controller>
    public IEnumerable<string> Get()
    {
        return TestService.GetSomething();
        //return new string[] { "value1", "value2" };
    }
}