Dependency
Injection (DI) is a software design pattern that promotes loosely coupled code
by allowing dependencies to be injected into a class from the outside, rather
than being created or managed within the class. In ASP.NET MVC 4, you can
implement DI using various DI containers such as Unity, Ninject, or Simple
Injector. Here, I'll provide an example using Unity for dependency injection.
Step 1: Create an ASP.NET MVC 4 Project If you haven't already, create a new
ASP.NET MVC 4 project in Visual Studio.
Step 2: Install Unity Container You need to install the Unity NuGet
package to your project. Open the Package Manager Console and run:
Install-Package Unity.Mvc4
Step 3:
Create a Dependency
Let's assume you have a service that you want to inject into your controller.
First, create an interface and a class for this service:
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// IService.cs
public interface IService
{
string GetData();
}
// Service.cs
public class Service : IService
{
public string GetData()
{
return "Hello from Service!";
}
}
Step 4:
Configure Dependency Injection In your Global.asax.cs file, configure Unity
to manage the dependencies. Add the following code to the Application_Start
method:
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protected void Application_Start()
{
AreaRegistration.RegisterAllAreas();
FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
RouteConfig.RegisterRoutes(RouteTable.Routes);
// Configure Unity Container
var container = new UnityContainer();
container.RegisterType<IService, Service>();
// Set the Unity DependencyResolver
DependencyResolver.SetResolver(new UnityDependencyResolver(container));
}
This code
sets up the Unity container and tells it that when someone asks for an IService,
it should provide an instance of the Service class.
Step 5: Inject the Dependency Now, you can inject the dependency
into your controller. Here's an example:
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public class HomeController : Controller
{
private readonly IService _service;
// Constructor injection
public HomeController(IService service)
{
_service = service;
}
public ActionResult Index()
{
string data = _service.GetData();
return View(data);
}
}
By
using constructor injection, the IService
is automatically injected when an instance of HomeController is created.
Step
6: Use the Dependency in a View In your view (Index.cshtml), you can display
the data from the injected service:
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@model string
<!DOCTYPE html>
<html>
<head>
<title>Dependency Injection Example</title>
</head>
<body>
<h1>@Model</h1>
</body>
</html>
When
you run the application, the text from the Service will be displayed on the Index page.
This is a basic example of implementing Dependency
Injection in ASP.NET MVC 4 using the Unity container. It promotes better
separation of concerns and testability by allowing you to easily switch out
dependencies and mock them during unit testing.
