Dependency Injection with UNITY and MEF in ASP.NET MVC

Step IV: Initialize Unity

 Hook up the unity bootstrapper in Application_start()

using System.Web;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;
using UnityIoC;

namespace TestUnityIoC
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
            Bootstrapper.Initialise(".\\bin", "TestUnityIoC.*.dll");

        }
    }
}

Step V: Export the Types

The assembly needs to emit the types for registration which is done as following. This code resides in "Service" folder.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using UnityIoC;
using System.ComponentModel.Composition; 

namespace TestUnityIoC
{
    [Export(typeof(IRegistrationType))]
    public class IoCContainerInit : IRegistrationType
    {
        #region "Variables"
        #endregion

        #region "Properties"
        #endregion

        #region "Constructor"
        #endregion

        #region "Public/Protectd Methods"
        public void Initialize(ITypeRegistrar registrar)
        {
            registrar.RegisterType<ITestService, TestService>();
        }
        #endregion

        #region "Private/Helper methods"
        #endregion
    }
}

Step VI: Test the DI for type participating in IoC. The code in"HomeController"is depicted below.  Please see the constructor.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace TestUnityIoC.Controllers
{
    public class HomeController : Controller    {

        private ITestService testService;

        public HomeController(ITestService testServiceForDI)
        {
            testService = testServiceForDI;
        }
        public ActionResult Index()
        {
            return View();
        }
        public ActionResult About()
        {
            ViewBag.Message = "Your application description page.";

            return View();
        }
        public ActionResult Contact()
        {
            ViewBag.Message = "Your contact page.";

            return View();
        }
    }
}

So far so good. Let’s try executing it.

Oops!!! It is not running successfully. What went wrong?

Mostly it looks like that the CLR is not able to find the type mapping. Please see the Fig#2 for the pattern. "TestUnityIoC.*.dll" is the root cause. The assembly is not found where types are registered.

It needs to be corrected as following.

using System.Web;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;
using UnityIoC;

namespace TestUnityIoC
{
    public class MvcApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            AreaRegistration.RegisterAllAreas();
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
            Bootstrapper.Initialise(".\\bin", "TestUnityIoC.dll");

        }
    }
}

And now, executing the projects, yields following result.

Conclusion and Summary

This small library offers ability to types themselves to be declared for registered for DI. Though this also needs an initialize or class for registration of all types in an assembly, the common file at solution level (centralized registration) is not needed more for carrying out the type registration. This also helps to give the ability for type registration to the assembly writers. This eliminates the need to compile the assembly containing centralized registration and just need of compile the assembly containing types.

Though this way multiple class constructs would be needed at different participating assemblies, dependency on centralized registration is eliminated.