Understanding Dependency Injection in C#

Published: 2024-03-12

Dependency Injection (DI) is a core concept in object-oriented programming. It refers to a technique where dependencies are provided to a class from the outside—typically via a constructor—rather than the class creating them itself.

Why is this useful? Because DI leads to more flexible, testableand maintainable applications.

Why Use Dependency Injection?

✅ Separation of Concerns

With DI, the responsibility for creating dependencies is separated from their usage. A class doesn’t need to know how to create its dependencies—it just receives them ready to use.

✅ Testability

DI makes unit testing easier. You can mock dependencies like DbContext, services, or repositories and inject them into your test subject. This allows for isolated and reliable tests.

✅ Flexibility and Extensibility

Your code becomes easier to extend or change. If a dependency changes, you don’t need to search through multiple files—you just inject a new implementation where needed.

Ways to Implement DI in C#

Here are three common approaches:

1. Constructor Injection (Recommended)

The most common and preferred way.

public class OrderService
{
    private readonly IOrderRepository _orderRepository;

    public OrderService(IOrderRepository orderRepository)
    {
        _orderRepository = orderRepository;
    }

    // OrderService methods...
}

2. Property Injection

Less commonly used, but sometimes helpful in frameworks like ASP.NET Core.

public class OrderService
{
    public IOrderRepository OrderRepository { get; set; }

    // OrderService methods...
}

3. Method Injection

Useful when a dependency is only needed temporarily.

public class OrderService
{
    public void SetOrderRepository(IOrderRepository orderRepository)
    {
        // Set the dependency
    }

    // OrderService methods...
}

Summary

Dependency Injection is all about externalizing object creation to promote cleaner architecture. It improves testability, modularityand overall code quality.

If you're building applications in C#, learning DI (and using it with tools like Microsoft.Extensions.DependencyInjection or Autofac) will take your design to the next level.

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