Example of container free DI with ASP.NET MVC

containerfree.cs

    public class MvcApplication : System.Web.HttpApplication
    {
        // Everthing else...

        protected void Application_Start()
        {
            // Everthing else...

            ControllerBuilder.Current.SetControllerFactory(new CustomControllerFactory(new BuildControllers()));
        }
    }

    public class CustomControllerFactory : DefaultControllerFactory
    {
        private readonly IBuildControllers controllerBuilder;

        public CustomControllerFactory(IBuildControllers controllerBuilder)
        {
            this.controllerBuilder = controllerBuilder;
        }

        protected override IController GetControllerInstance(System.Web.Routing.RequestContext requestContext, Type controllerType)
        {
            if (controllerType == null)
                throw new HttpException(404, string.Format("Controller was not found"));
            
            return controllerBuilder.FetchFromCache(controllerType);
        }
    }

    public class BuildControllers : IBuildControllers
    {
        private readonly IDictionary<Type, Func<IController>> controllerRegister;

        public BuildControllers()
        {
            // If anything in here got too complex, then clearly like any other code, you'd refactor and extract.

            // The following are application scoped, because this is called at application start

            var barConnectionString = ConfigurationManager.ConnectionStrings["Default"].ConnectionString;
            var barConnection = new SqlConnection(barConnectionString);
            var barService = new Lazy<BarService>(() => new BarService(barConnection));

            // Anything newed in a func will be unique for each invocation of that func, so will be request scoped like the controller
            // Give objects objects with longer lifetimes, but not shorter ones, as an object will live as long as a reference is held to it
            controllerRegister =
                new Dictionary<Type, Func<IController>>
                    {
                        {typeof (FooController), () => new FooController()}, // With no args
                        {typeof (HomeController), () => new HomeController(new FizzCalculator())}, // With one, request scoped arg
                        {typeof (BazController), () => new BazController(barService.Value)}, // With one, application scoped arg
                    };
        }

        public IController FetchFromCache(Type typeOfControllerToBuild)
        {
            try
            {
                return controllerRegister[typeOfControllerToBuild]();
            }
            catch (Exception)
            {
                throw new HttpException(404, string.Format("Controller of type {0} cannot be built.", typeOfControllerToBuild.FullName));
            }
        }
    }