Constructor Dependency injection in asp.net core 2

Question

I have read this official documentation: https://docs.microsoft.com/en-us/aspnet/core/fundamentals/dependency-injection.

There is something i do not understand in constructor injection:

Let's have a look to my code, which works fine:

public class HomeController : Controller
{
    private readonly UserManager<Utilisateurs> _userManager;
    private readonly SignInManager<Utilisateurs> _signInManager;
    private readonly RoleManager<IdentityRole> _roleManager;

    public HomeController(
        SignInManager<Utilisateurs> signInManager,
        UserManager<Utilisateurs> userManager,
        RoleManager<IdentityRole> roleManager)
    {
        _userManager = userManager;
        _signInManager = signInManager;
        _roleManager = roleManager;
    }

It works fine too if change constructor parameter orders or if i remove some parameters like this:

public class HomeController : Controller
{
    private readonly UserManager<Utilisateurs> _userManager;
    private readonly SignInManager<Utilisateurs> _signInManager;

    public HomeController(
        UserManager<Utilisateurs> userManager
        SignInManager<Utilisateurs> signInManager,
        )
    {
        _userManager = userManager;
        _signInManager = signInManager;
    }

I have understood the concept of DI. What i do not understand is how does it works in C# to have something dynamic in constructor parameters ? Is there a set of all kind of overload constructors ?

Thanks

You need to clarify your question. What do you mean by `have something dynamic in constructor parameters`? Are you referring to the `dynamic` key word? — Nkosi, Nov 30 '17 at 09:36
Might help to look at what a really simple [hand-rolled](https://stackoverflow.com/questions/15715978/simple-dependency-resolver#15717047) DI implementation actually does - nothing particularly clever is required. Obviously fully-fledged DI frameworks are more evolved, but at their core, they are just doing the same thing. — Cake or Death, Nov 30 '17 at 09:56

score 2 · Accepted Answer · answered Nov 30 '17 at 10:05

how does it work in C# to have something dynamic in constructor parameters ? Is there a set of all kind of overload constructors?

Don't use "dynamic" like that, it's a buzzword in that sentence. In programming, everything is dynamic.

If you mean to ask how a DI framework can match up registered services with constructor parameters, then yes, there is a set of constructor overloads.

The DI framework finds these through reflection, see MSDN: Type.GetConstructors(). Then for each constructor, the framework obtains the parameters of each constructor, matches those up with the registered services and invokes one of the constructors.

Constructor Dependency injection in asp.net core 2

1 Answers1