How do IoC controllers actually work? Specifically in .NET MVC?

Question

Controller Constructor:

    IRestaurantData db;

    public HomeController(IRestaurantData db)
    {
        this.db = db;
    }

// Container code

 public class ContainerConfig
{
    internal static void RegisterContainer(HttpConfiguration httpConfiguration)
    {
        var builder = new ContainerBuilder();
        builder.RegisterControllers(typeof(MvcApplication).Assembly);
        builder.RegisterApiControllers(typeof(MvcApplication).Assembly);

        builder.RegisterType<InMemoryRestaurantData>()
            .As<IRestaurantData>()
            .SingleInstance();

        var container = builder.Build();
        // MVC CONTROLLER VERSION
        DependencyResolver.SetResolver(new AutofacDependencyResolver(container));
        // WEBAPI CONTROLLER VERSION
        httpConfiguration.DependencyResolver = new AutofacWebApiDependencyResolver(container);
    }
}

So I'm trying to wrap my head around how Inversion of Control containers work. The course I'm in is using Autofac to create these containers. From what I'm currently understanding creating this container is making it so that when I instantiate my HomeController with IRestaurantData the container is pointing the interface AT InMemoryResataurantData everytime it is used. I can understand that much. What Im also confused by is I dont understand WHERE in the program my Controllers are are actually being instantiated? Does anyone know?

Answer 1

That is being done by autofac. whenever you request a class from a container, it will instantiate the type for you using the default constructor. If you have a constructor with parameters, it will look in the container for other registered types and will instantiate a new object or fetch an already used object.

Your instantiated types can be transient (short lived) or not.

So in short; when the object is requested.