How to subscribe to an event on a service in Angular2?

I know how to raise an event with the EventEmitter. I can also attach a method to be called if I have a component like this:

<component-with-event (myevent)="mymethod($event)" />

When I have a component like this, everything works great. I moved some logic into a service and I need to raise an event from inside the Service. What I did was this:

export class MyService {
myevent: EventEmitter = new EventEmitter();


someMethodThatWillRaiseEvent() {
this.myevent.next({data: 'fun'});
}
}

I have a component that needs to update some value based on this event but i can't seem to make it work. What I tried was this:

//Annotations...
export class MyComponent {
constructor(myService: MyService) {
//myService is injected properly and i already use methods/shared data on this.
myService.myevent.on(... // 'on' is not a method <-- not working
myService.myevent.subscribe(.. // subscribe is not a method <-- not working
}
}

How do i make MyComponent subscribe to the event when the service that raises it is not a component?

I'm on On 2.0.0-alpha.28

EDIT: Modified my "working example" to actually work, so focus can be put on the not-working part ;)

Example code: http://plnkr.co/edit/m1x62WoCHpKtx0uLNsIv

200557

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最佳答案

Update: I have found a better/proper way to solve this problem using a BehaviorSubject or an Observable rather than an EventEmitter. Please see this answer: https://stackoverflow.com/a/35568924/215945

Also, the Angular docs now have a cookbook example that uses a Subject.

Original/outdated/wrong answer: again, don't use an EventEmitter in a service. That is an anti-pattern.

Using beta.1... NavService contains the EventEmiter. Component Navigation emits events via the service, and component ObservingComponent subscribes to the events.

nav.service.ts

import {EventEmitter} from 'angular2/core';
export class NavService {
navchange: EventEmitter<number> = new EventEmitter();
constructor() {}
emitNavChangeEvent(number) {
this.navchange.emit(number);
}
getNavChangeEmitter() {
return this.navchange;
}
}

components.ts

import {Component} from 'angular2/core';
import {NavService} from '../services/NavService';


@Component({
selector: 'obs-comp',
template: `obs component, item: \{\{item}}`
})
export class ObservingComponent {
item: number = 0;
subscription: any;
constructor(private navService:NavService) {}
ngOnInit() {
this.subscription = this.navService.getNavChangeEmitter()
.subscribe(item => this.selectedNavItem(item));
}
selectedNavItem(item: number) {
this.item = item;
}
ngOnDestroy() {
this.subscription.unsubscribe();
}
}


@Component({
selector: 'my-nav',
template:`
<div class="nav-item" (click)="selectedNavItem(1)">nav 1 (click me)</div>
<div class="nav-item" (click)="selectedNavItem(2)">nav 2 (click me)</div>
`,
})
export class Navigation {
item = 1;
constructor(private navService:NavService) {}
selectedNavItem(item: number) {
console.log('selected nav item ' + item);
this.navService.emitNavChangeEvent(item);
}
}

Plunker