CODEWITHSUNDEEP
c#asp.net-core
Lord Vermillion
Lord Vermillion

Reputation: 5424

asp.net mvc core dependency injection constructor parameter

I'm trying to understand dependency injection in ASP.NET MVC CORE.

All examples are the same, they show to register HttpContextAccessor

public void ConfigureServices(IServiceCollection services)
{
    services.AddMvc();
    services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
}

Then the class that wants to access it:

public class UserService : IUserService
{
    private readonly IHttpContextAccessor _httpContextAccessor;

    public UserService(IHttpContextAccessor httpContextAccessor)
    {
        _httpContextAccessor = httpContextAccessor;
    }

    public bool IsUserLoggedIn()
    {
        var context = _httpContextAccessor.HttpContext;
        return context.User.Identities.Any(x => x.IsAuthenticated);
    }
}

But then, when i actually want to create an instance of UserService, it asks for the httpContextAccessor object in constructor, where do i get that from?

Upvotes: 3

Views: 844

Answers (2)

poke
poke

Reputation: 388313

When using dependency injection, you are not supposed to actually create any service yourself. To consume your UserService, you should just inject that somewhere as well.

Typically, the flow in ASP.NET Core for your application code starts in a controller. So if you want to use the UserService inside of a controller action, you should inject it into the controller:

public class ExampleController : Controller
{
    private readonly IUserService _userService;

    public ExampleController(IUserService userService)
    {
        _userService = userService;
    }

    public IActionResult Index()
    {
        var isLoggedIn = _userService.IsUserLoggedIn();

        // …

        return View();
    }
}

So you don’t create an instance yourself using new but instead you rely on the dependency injection system to provide you with an instance.

You just need to make sure to register the service inside of the ConfigureServices:

services.AddTransient<IUserService, UserService>();

This principle holds regardless of where you are within your application. Since the entry point is always being created by the system, you are always inside of a dependency injection context, so you can just depend on things which have dependencies themselves (which again could have more dependencies etc).

I would strongly suggest you to read the chapter on dependency injection of the documentation, as it covers the idea very well. It also explains what the different lifetimes mean.

Upvotes: 6

Derviş Kayımbaşıoğlu
Derviş Kayımbaşıoğlu

Reputation: 30665

in DI, you normally dont need to create Instance by yourself. Instead you need to register your implemented services to the DI service container and then call it inside your constructor.

This way you eliminates the need for manual instance creation.

services.AddScoped<IMyService, MyService>();

then

class MyConsumerClass
{
    private readonly IMyService _myService;
    MyConsumerclass(IMyService myService)
    {
         _myService = myService;
    }
}

In this way, you don't need to care about what services is needed to be initialized (parameterized) into your constructor.

Upvotes: 0

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