Dependency injection (DI) is a software design pattern that allows you to create flexible, maintainable, and testable applications by promoting loose coupling between components. ASP.NET Core has built-in support for DI, but because you are a rebel, we’ll explore how to use Unity, a popular and powerful IoC (Inversion of Control) container, for dependency injection in an ASP.NET Core application.

Unity is a lightweight, extensible, and high-performance IoC container that can be easily integrated with ASP.NET Core to provide advanced dependency injection features. In this guide, we will walk through the necessary steps to configure and use Unity in your ASP.NET Core application.

Prerequisites

Before we dive into the implementation, ensure that you have the following prerequisites:

1. .NET Core SDK installed (version 3.1 or later)
2. A basic understanding of ASP.NET Core and dependency injection
3. Familiarity with Unity Container

Step 1: Install Unity Container and Unity.Microsoft.DependencyInjection Packages

First, you need to install the necessary Unity packages. In your ASP.NET Core project, use the following commands to install the required packages:

dotnet add package Unity
dotnet add package Unity.Microsoft.DependencyInjection

Step 2: Configure Unity as the Dependency Injection Container

Now, let’s replace the default DI container in your ASP.NET Core application with Unity. Open the Program.cs file and modify the Host.CreateDefaultBuilder() method as shown below:

using Unity.Microsoft.DependencyInjection;

// ...

public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .UseUnityServiceProvider() // Add this line
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

By calling UseUnityServiceProvider(), we configure the application to use Unity as the DI container.

Step 3: Register Dependencies in Unity Container

Next, you need to register your dependencies in the Unity container. In the Startup.cs file, add a new method named ConfigureContainer:

using Unity;

// ...

public class Startup
{
    // ...

    public void ConfigureContainer(IUnityContainer container)
    {
        // Register your dependencies here, for example:
        // container.RegisterType<IMyService, MyService>();
    }
}

In the ConfigureContainer method, you can register your dependencies using the RegisterType method. This will tell Unity how to resolve the dependencies when required.

Step 4: Inject and Use Dependencies in Your Application

With the dependencies registered in Unity, you can now inject them into your application components, such as controllers, services, or middleware. For example, let’s inject a sample service into a controller:

public class MyService : IMyService
{
    public string GetMessage() => "Hello, Unity!";
}

public interface IMyService
{
    string GetMessage();
}

public class HomeController : Controller
{
    private readonly IMyService _myService;

    public HomeController(IMyService myService)
    {
        _myService = myService;
    }

    public IActionResult Index()
    {
        ViewBag.Message = _myService.GetMessage();
        return View();
    }
}

In this example, we inject IMyService into the HomeController and use it to set a message in the ViewBag. Unity will take care of resolving the correct implementation of IMyService when creating the controller instance.