在哪里注册Angular 2服务，以便可以在全球范围内使用它？

Question

I have a Service, say ServiceA, that performs a lot of server communication work. This service is used heavily by other services, including ServiceB, throughout the application. Is there a way that I can register it once (ie. in the App Component) such that it is available to all services that are being registered in child Components? Right now it seems that I have to register it alongside each Service that calls it.

When I add ServiceA to the viewProviders array of the AppComponent, I'm getting a No provider for ServiceA! exception when the injector tries to inject ServiceB into a child component.

AppComponent

 @Component({
  moduleId: module.id,
  selector: 'app1',
  viewProviders: [..., **ServiceA**],<--I WANT TO DO THIS SO ITS AVAILABLE EVERYWHERE
  templateUrl: 'app.component.html',
  directives: [...]
})
export class AppComponent {}

ServiceA

@Injectable()
export class ServiceA {
    constructor(http: Http) {}
}

ServiceB

@Injectable()
export class ServiceB {
    constructor(serviceA: ServiceA) {}
}

ChildComponent

 @Component({
  moduleId: module.id,
  selector: 'app1',
  viewProviders: [ServiceB,**ServiceA**], <-AND I DON'T WANT TO HAVE TO DO THIS EVERY TIME
  templateUrl: 'app.component.html',
  directives: [...]
})
export class ChildComponent {
    constructor(private serviceB, ServiceB) {}
}

Answer 1

The best way to inject a service is the same as you are currently doing, except that instead of injecting it via the viewProviders in the AppComponent, use the providers option. You will only have to include the providers option in the root component, but you will have to remember to import the service on each file and inject it in the constructor.

@Component({
    moduleId: module.id,
    selector: 'app1',
    providers: [ServiceA],
    templateUrl: 'app.component.html',
    directives: [...]
})
export class AppComponent {}