Ionic 4 Observables

Question

I have been trying to implement the rxjs Observable pattern in a Ionic 4 upgrade project with no success and I would like to know how to successfully implement Observable so that the expected result would be displayed on-screen.

This is the old way of doing things and somewhere 'user:loggedIn' is used to display x results on-screen.

 events.subscribe('user:loggedIn', (userEventData) => {
   this.getUserInfo(userEventData);
   this.registerPushNotifications();
   this.registerPushNotificationHandlers();
 });

Two ways implemented and tested but no results are displayed.

Method 1:

    let userLoggedIn = new Observable((observer) => {
      // const {next, error} = observer;

      observer.next({'user:loggedIn':observer});
      observer.complete();
    });

    userLoggedIn.subscribe((userEventData) => {
      console.log(userEventData)
      this.getUserInfo(userEventData);
      this.registerPushNotifications();
      this.registerPushNotificationHandlers();
    });

Method 2:

    var observer: Observable<any> = of();
    observer.subscribe(userEventData => {
      this.getUserInfo(userEventData);
      this.registerPushNotifications();
      this.registerPushNotificationHandlers();
    });

Is there a way to have the same functionality as the old Ionic events functionality in Ionic 4 using Observable or Subject implementations?

Answer 1

Here's one approach that might work for you. In your auth service you can create a private BehaviorSubject property to store the last value of a private login property. Then you can create a public observable with the BehaviorSubject as its source. Finally you can subscribe to the service's public observable in your page/component which can get and set whatever you need when the change to the state of the login property occurs. Here's a simple example of how it could work:

loginService.ts

export class LoginService {
  private login: boolean = false;
  private loginSubject$ = new BehaviorSubject<boolean>(this.login);
  loginChanged$ = this.loginSubject$.asObservable();

  constructor() { }

  updateLogin(){
    this.login = !this.login;
    this.loginSubject$.next(this.login);
  }
}

home.page.ts

export class HomePage implements OnInit, OnDestroy {

  timesClicked:number=0;
  loginButtonText:string;

  loginChangedSubscription: Subscription

  constructor(private loginService: LoginService) {}

  ngOnInit() {
    this.loginChangedSubscription = this.loginService.loginChanged$.subscribe((loginValue)=>{
      this.timesClicked += 1;
      this.loginButtonText =  (loginValue ? "Log Me Out" : "Log Me In");
    })
  }

  ngOnDestroy(): void {
    if (this.loginChangedSubscription) {
      this.loginChangedSubscription.unsubscribe();
    }
  }

  updateLogin():void{
    this.loginService.updateLogin();
  }
}

Just to show it working .... home.page.html

<ion-content>
  <ion-item>
    <ion-label>
      {{timesClicked}}
    </ion-label>
  </ion-item>
  <ion-button color="primary" (click)="updateLogin()">{{loginButtonText}}</ion-button>
</ion-content>

Hope this helps.