What is the best way to share services across Modules in angular2

Question

I am using an application structure as mentioned below

index.ts
|-app.module.ts
|-app.component.ts
|--hero (directory)
   |-hero.module.ts
   |-hero.ts (Data Object)
   |-hero.service.ts
   |-hero.component.ts
   |-index.ts (this file exports data obj, service, component & module)
|--dashboard (directory)
   |-dashboard.module.ts
   |-dashboard.component.ts
   |-index.ts (this file exports module and component)

I wish to use hero service in dashboard component. Below is the code snippet I am using right now and its working as expected. But not sure if its a good practice.

import { Component, OnInit } from '@angular/core';

import { Hero, HeroService } from '../hero/index';
import {Router} from '@angular/router';

@Component({
    moduleId: module.id,
    selector: 'my-dashboard',
    templateUrl: 'dashboard.component.html',
    styleUrls: ['dashboard.component.css']
})
export class DashboardComponent implements OnInit {
    heroes: Hero[] = [];

    constructor(private heroService: HeroService, private router: Router) { }

    ngOnInit(): void {
        this.heroService.getHeroes()
            .then(heroes => this.heroes = heroes.slice(1, 5));
    }

    gotoDetail(hero: Hero): void {
        let link = ['/detail', hero.id];
        this.router.navigate(link);
    }
}

I am curious to know if there is any way that I can access HeroService with reference to HeroModule rather than separately importing Hero object and HeroService from ../hero/index

Answer 1

from Range.io

So far our problem is that we are creating two instances of the same services in different levels of the DI tree. The instance created in the lower branch of the tree is shadowing the one defined at the root level. The solution? To avoid creating a second instance in a lower level of the DI tree for the lazy loaded module and only use the service instance registered at the root of the tree.

import { NgModule, ModuleWithProviders } from '@angular/core';
import { CounterService } from './counter.service';

@NgModule({})
export class SharedModule {
  static forRoot(): ModuleWithProviders {
    return {
      ngModule: SharedModule,
      providers: [CounterService]
    };
  }
}

With this setup, we can import this module in our root module AppModule calling the forRoot method to register the module and the service.

...
import { SharedModule } from './shared/shared.module';

@NgModule({
  imports: [
    SharedModule.forRoot(),
    ...
  ],
  ...
})
export class AppModule {}

Answer 2

Services are shared across the entire application, so if you put it into a module, other component has acces to it. However, you still need to import the classes Hero and HeroService in component where you use them.

Imports at the top of a class and Modules has just a differents purpose.