DI is a design pattern that allows classes to receive their dependencies from an external source, promoting loose coupling and testability. ASP.NET Core has built-in support for DI.

Lifetime Scopes:

• Transient: A new instance of the dependency is created every time it’s requested.
• Scoped: A new instance is created once per HTTP request.
• Singleton: A single instance is created and shared throughout the application’s lifetime.

public interface IMyService { string GetData(); }
public class MyService : IMyService { public string GetData() { return "Data from MyService"; } }

public void ConfigureServices(IServiceCollection services)
{
    services.AddTransient<IMyService, MyService>(); // Transient
    // services.AddScoped<IMyService, MyService>(); // Scoped
    // services.AddSingleton<IMyService, MyService>(); // Singleton
    services.AddControllers();
}

public class MyController : ControllerBase
{
    private readonly IMyService _myService;

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

    [HttpGet]
    public string Get()
    {
        return _myService.GetData();
    }
}

• The ConfigureServices method registers the IMyService with the DI container.
• The MyController constructor receives the IMyService dependency.