CODEWITHSUNDEEP
javascriptangular
Per Hornshøj-Schierbeck
Per Hornshøj-Schierbeck

Reputation: 15196

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

Upvotes: 132

Views: 227304

Answers (3)

ebey
ebey

Reputation: 153

Sometime quick fix of library cause that added event import like

import { EventEmitter } from 'events';

You must change it with core libray using subscribe

import { EventEmitter } from '@angular/core';

Upvotes: 0

Mark Rajcok
Mark Rajcok

Reputation: 364697

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Original/outdated/wrong answer: again, don't use an EventEmitter in a service.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

Upvotes: 164

Runeboy
Runeboy

Reputation: 79

Using alpha 28, I accomplished programmatically subscribing to event emitters by way of the eventEmitter.toRx().subscribe(..) method. As it is not intuitive, it may perhaps change in a future release.

Upvotes: 7

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