AspNet Core 1.1 Inject IOptions into a class - asp.net-core

Question

I am using the Options pattern in my AspNet Core 1.1 application. Everything is set according to the documentation:
public Startup(IHostingEnvironment env)
{
var builder = new ConfigurationBuilder()
.SetBasePath(env.ContentRootPath)
.AddJsonFile("appsettings.json", optional: false, reloadOnChange: true)
.AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true)
.AddEnvironmentVariables();
Configuration = builder.Build();
}
public void ConfigureServices(IServiceCollection services)
{
...
services.Configure<AppOptions>(Configuration);
...
}
I would like to inject the AppOptions class into a service that I am creating:
public class MyService
{
private readonly AppOptions options;
public MyService(IOptions<AppOptions> optionsAssesor)
{
options = optionsAssesor.Value;
}
...
}
My questions is: when I try to create an instance of the MyService class like:
MyService svc = new MyService();
I am getting an error saying that There is no argument given that corresponds to the required formal parameter optionsAssesor How can I take advantage of the DI and inject the AppOptions into my service?
I am kind of new to .NET Core so I am guessing I am missing something simple, but I cannot figure out what.
Thank you.

Answer 1

I am assuming that Service (MyService) is within scope of ASP.net core project.
You have to do following Thing.
public void ConfigureServices(IServiceCollection services)
{
services.AddScoped<MyService>();
... other things
}
Now Suppose that you are using your service ( or you want to use your service some controller then you have to do
public class HomeController : Controller
{
private MyService _myService = null;
public HomeController(MyService service)
{
_myService = service;
}
// now you can use _myService in your controller method.
}
Every thing like you have to go through Dependency.
Update 1
Now suppose you want to use it in another class then you can do like this.
For example another class is MyClass1.
public class MyClass1
{
private MyService _myService = null;
public MyClass1(MyService service)
{
_myService = service;
}
}
Now if I am thinking correct then if you are using ASP.net core then MyClass1 one way or other it will use by Controller. You have to register dependency for this.
services.AddScoped<MyClass1>(); // This should be in your ConfigureServices.

Answer 2

It depends on where you are trying to get an instance of MyService from. Basically you need to get a reference to the services collection (and register MyService in DI as well in startup), build a service provider, and then get the service. This will allow DI to construct an instance of MyService and pass it in an instance of AppOptions.
For example:
var provider = serviceCollection.BuildServiceProvider();
var myService = provider.GetService<MyService>();
That being said, in most places in ASP.NET Core you don't need to do this and are better off getting an instance of MyService through the Controller / Middleware constructor without having to build a Service Provider on your own.
You should look at the Microsoft Docs on Dependency Injection in ASP.NET core to further understand the different Service Lifetimes.