将局部变量值订阅到 Angular 中另一个组件中的变量的 Observable

Question

I want to change an HTML view via *ngIf , based on a local variable, which should change based on a variable delivered through an observable from a shared service.

HTML

<div class="login-container" *ngIf="!isAuthenticated">

TypeScript of same component:

export class LoginComponent implements OnInit {
  authenticationsSubscription;
  isAuthenticated: boolean;

  constructor(
    private authService: AuthServiceService,
    private router: Router,
    private route: ActivatedRoute){}

  getAuth(): Observable<boolean>{
    return this.authService.validation();
  }

  ngOnInit() {
    this.authenticationsSubscription = this.authService.validation().subscribe(auth => this.isAuthenticated = auth);
  }
} 

TypeScript of shared service AuthService :

export class AuthServiceService {
  isAuthenticated: boolean;

  validation(): Observable<boolean>{
    return of(this.isAuthenticated);
  }
}

While debugging I found out, the variable isAuthenticated in the LoginComponent does not change, on changes of the variable isAuthenticated of the AuthService. I also tried using pipe() and tap() , which did not change anything.

What am I doing wrong?

Answer 1

Convert your AuthServiceService to have the authentication state as a BehaviorSubject and return it as Observable as described below.

import { Observable, BehaviorSubject } from "rxjs";

export class AuthServiceService {
  private isAuthenticatedSub: BehaviorSubject<boolean> = new BehaviorSubject(false);

  set isAuthenticated(isAuthenticated: boolean) {
    this.isAuthenticatedSub.next(isAuthenticated);
  }

  get isAuthenticated(): boolean {
    return this.isAuthenticatedSub.value;
  }

  validation(): Observable<boolean> {
    return this.isAuthenticatedSub.asObservable();
  }
}

Answer 2

The actual subscription of your observable will only happens once, when the OnInit lifecycle hook is triggered when the component is initialized.

You can subscribe to a BehaviorSubject in order to catch value changes.

Stackblitz example

AuthService

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

@Injectable()
export class AuthService {
  isAuthenticated: BehaviorSubject<boolean>;

  constructor() {
    this.isAuthenticated = new BehaviorSubject<boolean>(false);
   }
}

Component

import { Component, OnInit } from '@angular/core';
import { AuthService } from './auth.service';
import { Observable } from 'rxjs';

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent implements OnInit {
  isAuthenticated: Observable<boolean>;

  constructor(private authService: AuthService) {}

  ngOnInit() {
    this.isAuthenticated = this.authService.isAuthenticated;
  }

  login() {
    this.authService.isAuthenticated.next(true);
  }

  logout() {
    this.authService.isAuthenticated.next(false);
  }
}

Template

<div *ngIf="isAuthenticated | async; else notAuthenticated">
  User is authenticated
  </div>

  <ng-template #notAuthenticated>
  <div>User isn't authenticated</div>
  </ng-template>

  <button (click)="login()">Login</button>
  <button (click)="logout()">Logout</button>