当我们在Angular 2中使用提供程序时？

Question

Some of examples From angular 2 documents they used for http also

import { HTTP_PROVIDERS }    from '@angular/http';
import { HeroService }       from './hero.service';
@Component({
  selector: 'my-toh',
  template: `
  <hero-list></hero-list>
  `,
  directives: [HeroListComponent],
  providers:  [
    HTTP_PROVIDERS,
    HeroService,
  ]
})

Answer 1

Providers need to be used to provide a way to create instances to inject. For example, if you want to inject an Http instance you need to have define the HTTP_PROVIDERS (that contains the provider for the Http type.

An important thing to understand is that Angular2 supports hierarchical injectors for dependency injector. I mean an injector is associated with each component and the current injector is a child injector of the injector of the parent component.

This question could interest you:

• What's the best way to inject one service into another in angular 2 (Beta)?