Dependency injection in ASP.NET MVC with Unity IoC Container


Download sample project (727,5KB)

Download sample project (546,3KB)

Update! This still apply in ASP.NET MVC 2 and Unity 2.0. Read more here...

Enabling truly easy testability with ASP.NET MVC Controllers requires a Dependency Injection container. This post is about showing a more real life example of combining Unity with ASP.NET MVC Controllers than the standard demo. Unity is the IoC Container from Microsoft Patterns & Practices and ships as a part of Enterprise Library as well as a stand alone on Codeplex.

We start with the unit test which drives the design of the controller.

public void Post_PostWithSlugExists_ReturnsResultWithPostAsModel() 
    controllerContext.RouteData.Values.Add("slug", ValidSlug); 
    var expected = MockRepository.GenerateStub(); 
    var blogPosts = new[] {expected}; 
    blogPostService.Expect(s => s.GetPostWhereSlugEquals(slug)) 
    var controller = CreateController();
    var result = (ViewResult) controller.Post(); 
    Assert.AreEqual(expected, result.ViewData.Model); 

Even though the test becomes a bit verbose it clearly states the intent of the controller’s Post method; given the right slug, a result is returned with a blog post as model.

Dependency Injection in ASP.NET MVC

In ASP.NET MVC every request starts in a controller which uses a set of dependencies to do its job. When we have applied Inversion of Control we can inject all of the controller’s dependencies either as a constructor argument or as a property setter. To fully take advantage of this technique we want the dependencies to be automatically injected without creating any of them in overloaded constructors or something like that. This is where the Controller Factory in ASP.NET MVC comes into play.

Controller Factory

In the System.Web.Mvc namespace lives the IControllerFactory which implementation is used by the framework to create controller instances. We can use this to swap out the default one and replace it with our own controller factory which uses Unity to create controllers instead.

Instead of implementing all of the IControllerFactory functionallity we can extend the System.Web.Mvc.DefaultControllerFactory and only override what we need.

public class UnityControllerFactory : DefaultControllerFactory 
    private readonly IUnityContainer container;
    public UnityControllerFactory(IUnityContainer container) { 
        this.container = container; 
    protected override IController GetControllerInstance(Type controllerType) { 
        return container.Resolve(controllerType) as IController; 

In the Global.asax, called MvcApplication in ASP.NET MVC by default, we create our Unity container and tells the MVC framework to use our UnityControllerFactory instead of the default one.

// in Global.asax.cs 
protected void Application_Start() 
    var container = new UnityContainer(); 
    var controllerFactory = new UnityControllerFactory(container); 


To illustrate why this is so powerful we will implement a controller that handles requests for blog posts, such as the one you’re reading right now. For this example the controller only handles requests for single blog posts using the post’s slug as identity. A slug is the post’s title made url friendly (e.g. "Dependency-injection-in-ASPNET-MVC-with-Unity-IoC-Container” for this post). The PostController has a dependency on an IBlogPostService which it uses to lookup the blog post to send to the view.

public class PostController : Controller 
    private readonly IBlogPostService blogPostService;
    public PostController(IBlogPostService blogPostService) 
        this.blogPostService = blogPostService; 
    public ActionResult Post() 
        var slug = GetSlug(); 
        var post = blogPostService.GetPostWhereSlugEquals(slug); 
        return View(post); 
    private string GetSlug() 
        return RouteData.GetRequiredString("slug"); 

Strongly-typed views

The Post action returns an ActionResult with the post a the model. We can use strongly-typed views to get intellisense in the aspx-file.

   1: <%@ Page /*...*/ Inherits="ViewPage" %>
   3: "Content1" ContentPlaceHolderID="TitleContent" runat="server">
   4:     <%=Model.Title %>
   7: "Content2" ContentPlaceHolderID="MainContent" runat="server">

<%=Model.Title %>


  10:         <%=Model.Body %>


<%=Html.PostActionLink("Permalink", Model) %>


"/2009/10/10/fail">fail link


Notice how the view inherits from ViewPage which is key to make the model type of IBlogPost. Then we can use the Post properties to render the blog post in the view.


Combining ASP.NET MVC with Unity or your IoC Container of choice makes your controllers much more easily testable. You only state your classes dependencies as constructor parameters or properties and the container will do the wiring for you. The gives you time to focus on the program logic and the interaction between its components.

Comments (3) -

  • Michael Wassermann

    2014-02-09 00:44:03 | Reply

    Hi, Could I see a working solution?

    I am getting an error.


    • Rickard

      2014-02-09 00:44:27 | Reply

      Sure. Sample project can be download at the top of the post.

      / Rickard

  • Unity dev

    2014-02-09 00:45:38 | Reply

    Looks like ILogWriter depenency cannot be resolved. Take away ILogWriter interface and code will work

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.