Ninject.MVC3, Nuget, WebActivator oh my

Question

I want to setup Ninject to do a simple test, as well as demonstrate the ease-of-setup using Nuget. I want to resolve a sample service.

public interface ITestService
{
    string GetMessage();
}
public class TestService : ITestService 
{
    public string GetMessage() { return "hello world"; }
}

I run the NuGet Install-Package NinjectMVC3 .... it nicely drops NinjectMVC3.cs into my App_Start folder, decorated with some WebActivator attributes to get it all loaded.

Next I add my binding in the NinjectMVC3.RegisterServices method:

private static void RegisterServices(IKernel kernel)
{
   kernel.Bind<ITestService>().To<TestServiceOne>();
}

Now I want to 'use' Ninjet to resolve my ITestService.

public ActionResult Index()
{
  //[Ninject, give me the service I need]
  ITestService service = ??? 

  ViewBag.Message = service.GetMessage();
  return View();
}

Is there another part to setting up Ninject? Do I need to provide a resolver?

What is the code I need to resolve my ITestService.

thanksasking help »

** * * * * * * * * * * * Update: * * * * * * * * * * * * * * * * **

Thanks for the great responses regarding 'controller constructor' injection. Simply adding a constructor with the ITestServcice as a param .... BAMM !!!

private ITestService _service;

public HomeController(ITestService service)
{
  _service = service
}
public ActionResult Index()
{
  ViewBag.Message = _service.GetMessage();
  return View();
}

Now what is the ideal solution for, when I need to get the Kernel directly.

var kernel = ... // Go grab the kernel from ????? (thanks Judah).
ITestService service = kernel.Get<ITestService>();

I can see the NinjectMVC3 class creates the Kernel, but does not hold or expose a reference to it, nor can I find a obvious class/method to 'get the kernel'.

I assume thee is a Ninject way to get it, but not sure.

** * * * * * * * * * * * (Final) Update: * * * * * * * * * * * * * * * * **

Thanks again for the answers and comments ....

Correction: The NinjectMVC3 class creates the Kernel, and does hold reference to the 'Bootstrapper', which as a IKernel on it.

So I added a 'resolve' method to the App_Start/NinjectMVC3 class ... works great.

public static class NinjectMVC3 /// created by the NinjectMVC3 NuGet  Packagae
{
   // add method to provide a global resolver.   
   public static T Resolve<T>()
   {
       return bootstrapper.Kernel.Get<T>();
   }
}

Paresh

This is certainly a matter of opinion, but the your NinjectMVC3.Resolve<T> static method is an example of the service locator anti-pattern. Generally speaking, dependency injection should be a "tell, don't ask" kind of thing. Mark Seemann discusses this on his blog, which might help clarify things a bit. blog.ploeh.dk/2010/02/03/ServiceLocatorIsAnAntiPattern.aspx – Fungiform

Answer 1

Add the ITestService as a constructor parameter to your controller:

private ITestService service;

public MyController(ITestService service)
{
   this.service = service;
}

public ActionResult Index()
{
  ViewBag.Message = this.service.GetMessage();
  return View();
}

Ninject will automatically inject the ITestService into your controller. Then use the service field inside your Index method.

---

Alternately, if you don't want Ninject to inject into your controller constructor, you can keep around the kernel you create, then inside your Index method, you call kernel.Get<ITestService>() to grab an instance:

public ActionResult Index()
{
  var kernel = ... // Go grab the kernel we created back in app startup.
  ITestService service = kernel.Get<ITestService>();

  ViewBag.Message = service.GetMessage();
  return View();
}

Have a look at Ninject dependency inject for controllers in MVC3.

Stringent

Thank-you, that makes sense. Now what would a good practice be for keeping the kernel around? Use a singleton as a global store? – Paresh

Personally, I have a static class called Dependency, with a single method: Get<T>. That internally calls the kernel's Get method. Consuming code then looks like: Dependency.Get<IFoo>() – Stringent

I would consider using the [Inject] parameter on the property instead of either a reference to the kernel, or the parameter-in-constructor approach. Adding constructors to your controllers will make for more verbose code if you have an interface on a base class that has to be passed in to every inherited constructor. ninject.codeplex.com/wikipage?title=Injection%20Patterns – Tempered

Answer 2

Steps:

1. Create a new ASP.NET MVC 3 project
2. Install the NuGet package from the Package Console: Install-Package Ninject.MVC3

3. In HomeController:

   public class HomeController : Controller
   {
       private readonly ITestService _service;
       public HomeController(ITestService service)
       {
           _service = service;
       }
   
       public ActionResult Index()
       {
           ViewBag.Message = _service.GetMessage();
           return View();
       }
   }
   

4. In App_Start/NinjectMVC3.cs:

   private static void RegisterServices(IKernel kernel)
   {
       kernel.Bind<ITestService>().To<TestService>();
   }       
   

Poorly

Thank-you, seems pretty straight forward. Now what would a good practice be for keeping the kernel around? Use a singleton as a global store? – Paresh