How to use BehaviourSubject to share the data to other components in Angular

ByAnkush Jain| Last Updated On Saturday, Apr 27, 2019

Angular

Disclaimer: I am a consultant at Amazon Web Services, and this is my personal blog. The opinions expressed here are solely mine and do not reflect the views of Amazon Web Services (AWS). Any statements made should not be considered official endorsements or statements by AWS.

We use BehaviourSubject to share the data with multiple components using a shared service.

For example, if we want to notify other components of the data change. Then we have to do two simple tasks.

We have to create a BehaviourSubject & an Observable of that BehaviourSubject in a service.
Secondly, we can subscribe to that Observable in other components.

I have created the below service to notify another component to log out the user from the application.

1. data.service.ts

Read the comments marked with 1, 2, 3 & 4 steps. They explain their usage itself.

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

//1. Import BehaviorSubject from rxjs module
import { BehaviorSubject } from 'rxjs/BehaviorSubject'

@Injectable({
  providedIn: 'root'
})
export class DataService {

  //2. Create the data which we want to share with all the components
  private logoutStatus = new BehaviorSubject(false);

  //3. Now we want to broadcast this message or data, so we create an observable
  getLogoutStatus = this.logoutStatus.asObservable();

  constructor() { }

  //4. Create a method that updates the data (Behaviour Subject)
  logoutUser(){
    this.logoutStatus.next(true);
  }
}

2. logout.ts

In this, the logoutUser() method of DataService will update the value of BehaviourSubject so that all & the observable (i.e. getLogoutStatus) of this BehaviourSubject will broadcast the message to all subscribers.

import { Component } from '@angular/core';
import { DataService } from './../../services/data.service'

@Component({
  selector: 'app-logout',
  templateUrl: './logout.component.html',
  styleUrls: ['./logout.component.scss']
})
export class LogoutComponent implements OnInit {

  constructor(private dataService : DataService) { }

  ngOnInit() {
    console.log("ngOnInit called");
  }

  onLogout(){
    this.dataService.logoutUser();
  }
}

3. app.component.ts

In this component, we have subscribed thegetLogoutStatus observable. The subscription handle will be executed every time whenever there is a change in the value of BehaviourSubject.

import { Component } from '@angular/core';
import { DataService } from './services/data.service';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss']
})
export class AppComponent {
  title = 'MyApp';

  constructor(private dataService : DataService) { }

  ngOnInit() {
    this.dataService.getLogoutStatus.subscribe((data) => {
      if(data === true){
        alert("User has been loggedout");
      }
    })
  }
}

How to use BehaviourSubject to share the data to other components in Angular

1. data.service.ts

2. logout.ts

3. app.component.ts

Ankush JainSoftware Engineer

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