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Jen-Hsuan Hsieh
Jen-Hsuan Hsieh

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Day 48 of #100DaysOfCode: Dependency Injection in ASP.NET MVC5 using Ninject

#csharp #100daysofcode #webdev #mvc

Introduction

The controller is tied to concrete implementation of service because the constructor of the HomeController has to create the instance of service.

public HomeController()
{
    _messageService = new MessageService();
}

public ActionResult About()
{
    ViewBag.Message = _messageService.GetWelcomeMessage();
    return View();
}
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There are a few advantages If we can decouple the controller with others.

  1. It'll be easier to test the controller when we want to mock the service.
  2. It'll ensure the single responsibility principle. It means that we only have to concern that how do we retrieving the data and not the concrete implementation.

Ninject is a Dependency Injection framework to break applications into loosely-coupled, highly-cohesive components, and then glue them back together.

Steps

1. Create a ASP.NET MVC project

2. Install packages 

Install-Package Ninject -Version 3.3.4
Install-Package Ninject.MVC5 -Version 3.3.0
Install-Package Ninject.Web.Common.WebHost -Version 3.3.2
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3. Create an interface 

public interface IMessageService
{
    string GetWelcomeMessage();
}
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4. Create a service implemented that interface 

public class MessageService : IMessageService
{
    public string GetWelcomeMessage()
    {
        return "Welcome to Ninject MVC5 Example";
    }
}
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5. Edit App_Start/NinjectWebCommon.cs

It will generate NinjectWebCommon.cs after installing packages automatically. Add the following code in CreateKernel()

private static IKernel CreateKernel()
{
    var kernel = new StandardKernel();
    try
    {
        kernel.Bind<Func<IKernel>>().ToMethod(ctx => () => new Bootstrapper().Kernel);
        kernel.Bind<IHttpModule>().To<HttpApplicationInitializationHttpModule>();
        kernel.Bind<IMessageService>().To<MessageService>();
        DependencyResolver.SetResolver(new NinjectDependencyResolver(kernel));
        RegisterServices(kernel);
        return kernel;
    }
    catch
    {
        kernel.Dispose();
        throw;
    }
}
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6. Edit Controllers/HomeController.cs

Now We can use dependency injection instead of creating instances in the controller.

public class HomeController : Controller
{
    private readonly IMessageService _messageService;
    public HomeController(IMessageService messageService)
    {
        _messageService = messageService;
    }
    ...
    public ActionResult About()
    {
        ViewBag.Message = _messageService.GetWelcomeMessage();

        return View();
    }
    ...
}
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That's it!

Articles

There are some of my articles and released projects. Feel free to check if you like!

References

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