What is dependency injection and how is it implemented in .NET?

Question

ICSM Computer · Answer

Dependency Injection (DI) is a design pattern used to achieve
loose coupling between classes by injecting dependencies from the outside, rather than a class creating its own dependencies.
Why Use Dependency Injection?
Improves testabilityEncourages modular designEnables inversion of control (IoC) — classes depend on abstractions, not implementations
Real-World Analogy
Instead of a class baking its own cake, it asks for a cake to be delivered.
Without Dependency Injection (Tightly Coupled)
public class OrderService
{
    private EmailService _emailService = new EmailService(); // tightly coupled
    public void ProcessOrder()
    {
        // business logic
        _emailService.SendEmail();
    }
}
With Dependency Injection (Loosely Coupled)
public interface IEmailService
{
    void SendEmail();
}
public class EmailService : IEmailService
{
    public void SendEmail() { /* send logic */ }
}
public class OrderService
{
    private readonly IEmailService _emailService;
    public OrderService(IEmailService emailService) // dependency injected
    {
        _emailService = emailService;
    }
    public void ProcessOrder()
    {
        _emailService.SendEmail();
    }
}
How It's Implemented in .NET (ASP.NET Core)
1. Register services in Startup.cs (or
Program.cs in .NET 6+)
services.AddScopedandlt;IEmailService, EmailServiceandgt;();
services.AddScopedandlt;OrderServiceandgt;();
2. Constructor injection (automatically handled by framework)
public class HomeController : Controller
{
    private readonly OrderService _orderService;
    public HomeController(OrderService orderService)
    {
        _orderService = orderService;
    }
    public IActionResult Index()
    {
        _orderService.ProcessOrder();
        return View();
    }
}
Types of DI in .NET
Type
Description
Constructor Injection
Most common, safe for required dependencies
Property Injection
Optional dependencies
Method Injection
Dependencies passed to methods
Lifetime Scopes
Method
Lifetime
AddSingletonandlt;Tandgt;()
One instance for the whole app
AddScopedandlt;Tandgt;()
One per request
AddTransientandlt;Tandgt;()
New instance every time it's requested
Benefits
Makes unit testing easier (e.g., mock services)Reduces tight couplingPromotes separation of concernsEnables inversion of control

interview

What is dependency injection and how is it implemented in .NET?

ICSM Computer

Can you answer this question?

1 Answers

Why Use Dependency Injection?

Real-World Analogy

Without Dependency Injection (Tightly Coupled)

With Dependency Injection (Loosely Coupled)

How It's Implemented in .NET (ASP.NET Core)

1. Register services in `Startup.cs` (or `Program.cs` in .NET 6+)

2. Constructor injection (automatically handled by framework)

Types of DI in .NET

Lifetime Scopes

Benefits

Liked By

Type	Description
Constructor Injection	Most common, safe for required dependencies
Property Injection	Optional dependencies
Method Injection	Dependencies passed to methods

Method	Lifetime
`AddSingleton<T>()`	One instance for the whole app
`AddScoped<T>()`	One per request
`AddTransient<T>()`	New instance every time it's requested

interview

What is dependency injection and how is it implemented in .NET?

ICSM Computer

Can you answer this question?

1 Answers

Why Use Dependency Injection?

Real-World Analogy

Without Dependency Injection (Tightly Coupled)

With Dependency Injection (Loosely Coupled)

How It's Implemented in .NET (ASP.NET Core)

1. Register services in Startup.cs (or Program.cs in .NET 6+)

2. Constructor injection (automatically handled by framework)

Types of DI in .NET

Lifetime Scopes

Benefits

Liked By

1. Register services in `Startup.cs` (or `Program.cs` in .NET 6+)