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How does the .NET dependency injection container and ASP.NET Core's model binding use reflection and attributes together under the hood?

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Answer

ASP.NET Core scans controller action parameters and constructor parameters via reflection, matching them against registered services (for DI) or incoming request data (for model binding) — attributes like [FromBody], [FromRoute], and [Required] on those parameters guide exactly HOW reflection-based binding should interpret and validate each one at request time.
public class UsersController : ControllerBase {
  private readonly IUserService _service; // resolved via reflection-based DI
  public UsersController(IUserService service) { _service = service; }

  [HttpPost]
  public IActionResult Create([FromBody] CreateUserRequest request) { /* ... */ }
}
Real-world example Understanding how ASP.NET Core 'magically' wires up your controller's dependencies and request parameters without you writing manual binding code.

Common follow-ups: Why is reflection-heavy DI/binding done ONCE at application startup rather than on every single request, for performance reasons?

Dependency Injection & IoC Principles
All 11 Attributes & Reflection questions