How to use factory provider?

Question

I need to inject a service into another service in an Angular 2 application.

After reading the docs I deduced, that the best approach is to use a Factory Provider. However, two questions have arisen:

1) The docs recommend the creation of a HeroServiceProvider class with two "code segments":

let heroServiceFactory = (logger: Logger, userService: UserService) => {
  return new HeroService(logger, userService.user.isAuthorized);
};

export let heroServiceProvider =
  { provide: HeroService,
    useFactory: heroServiceFactory,
    deps: [Logger, UserService]
  };

My question is how should the class generally look like? Where should one add the above code segments?

2) How should/could one use this factory? I see, it should be imported as:

import { heroServiceProvider } from './hero.service.provider';

@Component({
  selector: 'my-selector',
  template: `
  `,
  providers: [heroServiceProvider]
})

How could then the desired parametrized service retrieved and accessed?

Answer 1

I faced same issues to inject on app_initalizer, after long search i found the solution below. May be this is help for your scenario.

@NgModule({
  imports: [ BrowserModule],
  ...
  providers: [
    {
      provide: HeroService,
      useFactory: heroServiceFactory,
      deps: [Logger, UserService],
      multi: true
    }
    ]
})
export class AppModule {}


export function heroServiceFactory = (logger: Logger, userService: UserService) => {
    return new HeroService(logger, userService.user.isAuthorized);
};