How does ASP.NET MVC know how to fill your model to feed your Controller's Action? Does it involve reflection?

Question

Having defined a Model

public class HomeModel {
    [Required]
    [Display(Name = "First Name")]
    public string FirstName { get; set; }

    [Required]
    [Display(Name = "Surname")]
    public string Surname { get; set; }
}

and having the following Controller

public class HomeController : Controller {
    [HttpPost]
    public ActionResult Index(HomeModel model) {
        return View(model);
    }

    public ActionResult Index() {

        return View();
    }
}

by some "magic" mechanism HomeModel model gets filled up with values by ASP.NET MVC. Does anyone know how?

From some rudimentary tests, it seems it will look at the POST response and try to match the response objects name with your Model's properties. But to do that I guess it must use reflection? Isn't that inheritably slow?

Thanks

Answer 1

Yes, you are talking about the magic ModelBinder.

ModelBinder is responsible for creating a Model and hydrating it with values from the form post-back and performing validation which its result will appear in ModelState.

Default implementation is DefaultModelBinder but you can plug-in your own.