Dependency Injection (DI) is a fundamental concept in software engineering that enables developers to write loosely-coupled, maintainable, and testable code. In this blog post, we will discuss what Dependency Injection is and how to use it in ASP.NET Core MVC with .NET 6.

What is Dependency Injection?

Dependency Injection is a design pattern that enables the separation of concerns in a software application. It allows objects to be created with their dependencies injected into them rather than having the objects create their dependencies themselves. This approach makes it easier to maintain, test, and modify the code as the dependencies can be easily swapped without affecting the functionality of the objects.

In simpler terms, Dependency Injection is a way of providing the necessary dependencies to a class or a method, without the class or method needing to know how to create those dependencies. Instead, the dependencies are passed to the class or method by an external entity.

How to Use Dependency Injection in ASP.NET Core MVC with .NET 6

ASP.NET Core MVC is a powerful and flexible framework that supports Dependency Injection out-of-the-box. Here are the steps to use Dependency Injection in ASP.NET Core MVC with .NET 6:

The 4 roles in dependency injection

If you want to use this technique, you need classes that fulfill four basic roles. These are:

1. The service you want to use.

2. The client that uses the service.

3. An interface that’s used by the client and implemented by the service.

4. The injector which creates a service instance and injects it into the client.

Step 1: Add Services to the Dependency Injection Container

The first step is to register the services that you want to inject into your controllers, views, or other classes. In ASP.NET Core MVC, you can register services in the ConfigureServices method in the Startup.cs file. The ConfigureServices method is called when the application starts up and is used to configure the services that the application will use.

For example, let's say we want to register a service that calculates the total price of a shopping cart. We can define an interface and a class for this service as follows:

public interface IShoppingCartService
{
    decimal GetTotalPrice(IEnumerable<Product> products);
}

public class ShoppingCartService : IShoppingCartService
{
    public decimal GetTotalPrice(IEnumerable<Product> products)
    {
        decimal totalPrice = 0;

        foreach (var product in products)
        {
            totalPrice += product.Price;
        }

        return totalPrice;
    }
}

To register this service in the Dependency Injection container, we need to add the following code to the ConfigureServices method:

public void ConfigureServices(IServiceCollection services)
{
    services.AddScoped<IShoppingCartService, ShoppingCartService>();
    // other service registrations...
}

Here, we are using the AddScoped method to register the ShoppingCartService class as an implementation of the IShoppingCartService interface. The AddScoped method specifies that a new instance of the ShoppingCartService class will be created for each HTTP request.

Step 2: Inject Services into Controllers or Other Classes

Once the services are registered in the Dependency Injection container, we can inject them into controllers, views, or other classes using constructor injection.

For example, let's say we want to use the IShoppingCartService in a controller to calculate the total price of a shopping cart. We can define the controller as follows:

public class ShoppingCartController : Controller
{
    private readonly IShoppingCartService _shoppingCartService;

    public ShoppingCartController(IShoppingCartService shoppingCartService)
    {
        _shoppingCartService = shoppingCartService;
    }

    public IActionResult Index(IEnumerable<Product> products)
    {
        decimal totalPrice = _shoppingCartService.GetTotalPrice(products);
        return View(totalPrice);
    }
}

Here, we are using constructor injection to inject the IShoppingCartService into the controller. The _shoppingCartService field is assigned the instance of the ShoppingCartService class that was registered in the Dependency Injection container.

Conclusion

In conclusion, Dependency Injection is a powerful technique that can greatly improve the quality and maintainability of your ASP.NET Core MVC application. By separating the creation and management of dependencies from your code, you can create more flexible, testable, and maintainable applications that are easier to extend and update. With the built-in support for DI in .NET 6, it has never been easier to get started with this powerful pattern. By embracing Dependency Injection, you can take your application development skills to the next level and build better software that meets the needs of your users.