Is there no equivalent to $scope.emit() or $scope.broadcast() in Angular?
I know the EventEmitter functionality, but as far as I understand that will just emit an event to the parent HTML element.
What if I need to communicate between fx. siblings or between a component in the root of the DOM and an element nested several levels deep?
I have created a pub-sub sample here:
http://www.syntaxsuccess.com/viewarticle/pub-sub-in-angular-2.0
The idea is to use RxJs Subjects to wire up an Observer and and Observables as a generic solution for emitting and subscribing to custom events. In my sample I use a customer object for demo purposes
this.pubSubService.Stream.emit(customer);
this.pubSubService.Stream.subscribe(customer => this.processCustomer(customer));
Here is a live demo as well: http://www.syntaxsuccess.com/angular-2-samples/#/demo/pub-sub
Service Events: Components can subscribe to service events. For example, two sibling components can subscribe to the same service event and respond by modifying their respective models. More on this below.
But make sure to unsubscribe to that on destroy of the parent component.
DO Not Use EventEmitter for your service communication.
You should use one of the Observable types. I personally like BehaviorSubject.
Simple example:
You can pass initial state, here I passing null
let subject = new BehaviorSubject(null);
When you want to update the subject
subject.next(myObject)
Observe from any service or component and act when it gets new updates.
subject.subscribe(this.YOURMETHOD);
I'm using a message service that wraps an rxjs Subject (TypeScript)
Plunker example: Message Service
import { Injectable } from '@angular/core';
import { Subject } from 'rxjs/Subject';
import { Subscription } from 'rxjs/Subscription';
import 'rxjs/add/operator/filter'
import 'rxjs/add/operator/map'
interface Message {
type: string;
payload: any;
}
type MessageCallback = (payload: any) => void;
@Injectable()
export class MessageService {
private handler = new Subject<Message>();
broadcast(type: string, payload: any) {
this.handler.next({ type, payload });
}
subscribe(type: string, callback: MessageCallback): Subscription {
return this.handler
.filter(message => message.type === type)
.map(message => message.payload)
.subscribe(callback);
}
}
Components can subscribe and broadcast events (sender):
import { Component, OnDestroy } from '@angular/core'
import { MessageService } from './message.service'
import { Subscription } from 'rxjs/Subscription'
@Component({
selector: 'sender',
template: ...
})
export class SenderComponent implements OnDestroy {
private subscription: Subscription;
private messages = [];
private messageNum = 0;
private name = 'sender'
constructor(private messageService: MessageService) {
this.subscription = messageService.subscribe(this.name, (payload) => {
this.messages.push(payload);
});
}
send() {
let payload = {
text: `Message ${++this.messageNum}`,
respondEvent: this.name
}
this.messageService.broadcast('receiver', payload);
}
clear() {
this.messages = [];
}
ngOnDestroy() {
this.subscription.unsubscribe();
}
}
(receiver)
import { Component, OnDestroy } from '@angular/core'
import { MessageService } from './message.service'
import { Subscription } from 'rxjs/Subscription'
@Component({
selector: 'receiver',
template: ...
})
export class ReceiverComponent implements OnDestroy {
private subscription: Subscription;
private messages = [];
constructor(private messageService: MessageService) {
this.subscription = messageService.subscribe('receiver', (payload) => {
this.messages.push(payload);
});
}
send(message: {text: string, respondEvent: string}) {
this.messageService.broadcast(message.respondEvent, message.text);
}
clear() {
this.messages = [];
}
ngOnDestroy() {
this.subscription.unsubscribe();
}
}
The subscribe method of MessageService returns an rxjs Subscription object, which can be unsubscribed from like so:
import { Subscription } from 'rxjs/Subscription';
...
export class SomeListener {
subscription: Subscription;
constructor(private messageService: MessageService) {
this.subscription = messageService.subscribe('someMessage', (payload) => {
console.log(payload);
this.subscription.unsubscribe();
});
}
}
Also see this answer: https://stackoverflow.com/a/36782616/1861779
You can use EventEmitter or observables to create an eventbus service that you register with DI. Every component that wants to participate just requests the service as constructor parameter and emits and/or subscribes to events.
See also
The following code as an example of a replacement for $scope.emit() or $scope.broadcast() in Angular 2 using a shared service to handle events.
import {Injectable} from 'angular2/core';
import * as Rx from 'rxjs/Rx';
@Injectable()
export class EventsService {
constructor() {
this.listeners = {};
this.eventsSubject = new Rx.Subject();
this.events = Rx.Observable.from(this.eventsSubject);
this.events.subscribe(
({name, args}) => {
if (this.listeners[name]) {
for (let listener of this.listeners[name]) {
listener(...args);
}
}
});
}
on(name, listener) {
if (!this.listeners[name]) {
this.listeners[name] = [];
}
this.listeners[name].push(listener);
}
off(name, listener) {
this.listeners[name] = this.listeners[name].filter(x => x != listener);
}
broadcast(name, ...args) {
this.eventsSubject.next({
name,
args
});
}
}
Example usage:
Broadcast:
function handleHttpError(error) {
this.eventsService.broadcast('http-error', error);
return ( Rx.Observable.throw(error) );
}
Listener:
import {Inject, Injectable} from "angular2/core";
import {EventsService} from './events.service';
@Injectable()
export class HttpErrorHandler {
constructor(eventsService) {
this.eventsService = eventsService;
}
static get parameters() {
return [new Inject(EventsService)];
}
init() {
this.eventsService.on('http-error', function(error) {
console.group("HttpErrorHandler");
console.log(error.status, "status code detected.");
console.dir(error);
console.groupEnd();
});
}
}
It can support multiple arguments:
this.eventsService.broadcast('something', "Am I a?", "Should be b", "C?");
this.eventsService.on('something', function (a, b, c) {
console.log(a, b, c);
});
My favorite way to do is by using behavior subject or event emitter (almost the same) in my service to control all my subcomponent.
Using angular cli, run ng g s to create a new service then use a BehaviorSubject or EventEmitter
export Class myService {
#all the stuff that must exist
myString: string[] = [];
contactChange : BehaviorSubject<string[]> = new BehaviorSubject(this.myString);
getContacts(newContacts) {
// get your data from a webservices & when you done simply next the value
this.contactChange.next(newContacts);
}
}
When you do that every component using your service as a provider will be aware of the change. Simply subscribe to the result like you do with eventEmitter ;)
export Class myComp {
#all the stuff that exists like @Component + constructor using (private myService: myService)
this.myService.contactChange.subscribe((contacts) => {
this.contactList += contacts; //run everytime next is called
}
}
This is my version:
export interface IEventListenr extends OnDestroy{
ngOnDestroy(): void
}
@Injectable()
export class EventManagerService {
private listeners = {};
private subject = new EventEmitter();
private eventObserver = this.subject.asObservable();
constructor() {
this.eventObserver.subscribe(({name,args})=>{
if(this.listeners[name])
{
for(let listener of this.listeners[name])
{
listener.callback(args);
}
}
})
}
public registerEvent(eventName:string,eventListener:IEventListenr,callback:any)
{
if(!this.listeners[eventName])
this.listeners[eventName] = [];
let eventExist = false;
for(let listener of this.listeners[eventName])
{
if(listener.eventListener.constructor.name==eventListener.constructor.name)
{
eventExist = true;
break;
}
}
if(!eventExist)
{
this.listeners[eventName].push({eventListener,callback});
}
}
public unregisterEvent(eventName:string,eventListener:IEventListenr)
{
if(this.listeners[eventName])
{
for(let i = 0; i<this.listeners[eventName].length;i++)
{
if(this.listeners[eventName][i].eventListener.constructor.name==eventListener.constructor.name)
{
this.listeners[eventName].splice(i, 1);
break;
}
}
}
}
emit(name:string,...args:any[])
{
this.subject.next({name,args});
}
}
use:
export class <YOURCOMPONENT> implements IEventListener{
constructor(private eventManager: EventManagerService) {
this.eventManager.registerEvent('EVENT_NAME',this,(args:any)=>{
....
})
}
ngOnDestroy(): void {
this.eventManager.unregisterEvent('closeModal',this)
}
}
emit:
this.eventManager.emit("EVENT_NAME");
We implemented a ngModelChange observable directive that sends all model changes through an event emitter that you instantiate in your own component. You simply have to bind your event emitter to the directive.
See: https://github.com/atomicbits/angular2-modelchangeobservable
In html, bind your event emitter (countryChanged in this example):
<input [(ngModel)]="country.name"
[modelChangeObservable]="countryChanged"
placeholder="Country"
name="country" id="country"></input>
In your typescript component, do some async operations on the EventEmitter:
import ...
import {ModelChangeObservable} from './model-change-observable.directive'
@Component({
selector: 'my-component',
directives: [ModelChangeObservable],
providers: [],
templateUrl: 'my-component.html'
})
export class MyComponent {
@Input()
country: Country
selectedCountries:Country[]
countries:Country[] = <Country[]>[]
countryChanged:EventEmitter<string> = new EventEmitter<string>()
constructor() {
this.countryChanged
.filter((text:string) => text.length > 2)
.debounceTime(300)
.subscribe((countryName:string) => {
let query = new RegExp(countryName, 'ig')
this.selectedCountries = this.countries.filter((country:Country) => {
return query.test(country.name)
})
})
}
}
Source: Stackoverflow.com