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

In ASP.NET Core, Dependency Injection is a design pattern and a built-in feature provided by the framework for managing class dependencies. This helps in achieving loose coupling between classes and improves maintainability, testability, and reusability of the code.

Dependency Injection in ASP.NET Core is implemented using the built-in IoC (Inversion of Control) container, which is registered in the application's service collection during application startup. The container is responsible for creating instances of classes and injecting them into other classes where they are needed.

To implement Dependency Injection in ASP.NET Core, you first define the services (dependencies) that your application needs, then register those services in the IoC container using methods like `AddSingleton`, `AddTransient`, or `AddScoped` in the `Startup` class.

For example, you can register a service interface and its implementation as follows:

```html

services.AddSingleton<IMyService, MyService>();

```

You can then inject the registered services into your classes using constructor injection or property injection. The container automatically resolves the dependencies and provides the instances where needed.

```html

public class MyController
{
private readonly IMyService _myService;

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

// Controller actions
}

```

By following the Dependency Injection pattern in ASP.NET Core, you can write more modular and testable code, making your application more maintainable and scalable in the long run.