How to implement behavior subject using service in Angular 8

Question

I'm new to Angular and I'm having an issue.

I'm creating an app with several sibling components. When I update a value in one component other components don't update. I know that to resolve this issue I should use behaviour subject. But how do I implement it with my service, the components and all the templates?

Here is my code -

----------------------My service---------------------------

//import


@Injectable() 
export class CoachService {

    apiURL = environment.apiURL;

    constructor(private http: HttpClient ) { }

    coachProfile(token :string)
    {  
    return this.http.post<any>(this.apiURL+'/coach/profile_infos',{
      token: token
      })        
    }

    updateProfile(info: any, token: string, us_id: string) {
      return this.http.post<any[]>(this.apiURL + '/coach/update_profile', {
        token: token,
        us_id: us_id,
        us_lang: info.us_lang,
        us_firstname: info.us_firstname,
        us_lastname: info.us_lastname,
        us_sex: info.us_sex,
        us_birthdate: info.us_birthdate,
        us_national_number : info.us_national_number,
        us_email: info.us_email,
        us_gsm: info.us_gsm,        
        online_profile: info.online_profile,          
        us_address: info.us_address,
        us_zip: info.us_zip,
        us_city: info.us_city,
        country:{
          id: info.country.id
        }
        })

    } 

}

----------one component.ts-------------------

//import
//component decorator

export class CoordonneesComponent implements OnInit, OnDestroy {

private coachProfile;
  token: string = localStorage.getItem('token');
  us_id : string;
  us_lang: string; 
  infos_profile: any;
  online: any;


  constructor(private translate: TranslateService,private coachService: CoachService, private router: Router) { }

  ngOnInit() {

    this.coachProfile=this.coachService.coachProfile(this.token)
      .subscribe((data) => {
        this.infos_profile = data.results;
        this.online = this.infos_profile.online_profile;
        this.translate.use(this.infos_profile.us_lang)
        this.infos_profile.lang= this.infos_profile.us_lang;

      });

   .....
  }


updateCoordonees() {
  this.coachService.updateProfile(this.infos_profile, this.token, this.us_id)
    .subscribe((data: any) => {

      if(data.success && data.msg!=null)
      { 
  // do something
      }
      else
      {
       // do something
      }

    },
      (err) => {
        // do something
      });

}  



  ngOnDestroy() {
    this.countrieList.unsubscribe();
    this.coachProfile.unsubscribe();  
  }


}

Mauricio Gracia Gutierrez · Accepted Answer · 2021-07-13 03:45:48Z

50

I'm going to show you a simple way:

@Injectable() 
export class ProfileService {

    private profileObs$: BehaviorSubject<Profile> = new BehaviorSubject(null);

    getProfileObs(): Observable<Profile> {
        return this.profileObs$.asObservable();
    }

    setProfileObs(profile: Profile) {
        this.profileObs$.next(profile);
    }
}

Now when you update something anywhere in the application, you can set that change by the ProfileService and each subscriber is receiving the change. I recommend you subscribe in ngOnInit.

ngOnInit() {
  this.profileService.getProfileObs().subscribe(profile => this.profile = profile);
}

Never forget to unsubscribe from the observables to prevent memory leaks!

There are many ways u can do that --> Use a subscription and unsubscribe in ngOnDestroy() or use another subject and deliver it to takeUntil like this:

unsubscribe$: Subject<boolean> = new Subject();

...

ngOnInit() {    
  this.profileService.getProfileObs()
                     .pipe(takeUntil(this.unsubscribe$))
                     .subscribe(profile => this.profile = profile);
}

ngOnDestroy() {
  this.unsubscribe$.next(true);
  this.unsubscribe$.complete();
}

edited Jul 13, 2021 at 3:45

Mauricio Gracia Gutierrez

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answered Aug 5, 2019 at 9:15

sagat

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3 Comments

kkD97 Over a year ago

Thanks foryour explanation. I'll close this subject

juanjinario Over a year ago

Why you have to convert the response to asObservable()? is it not inherit?

sagat Over a year ago

This is a convenient answer to your question: stackoverflow.com/questions/36986548/…

Robert garcia · Accepted Answer · 2019-08-05 09:07:58Z

First create a BehaviourSubject

this._source = new BehaviourSubject<yourType>(initialValue);
this.source = this._source.asObservable();

Define a function to "update" the BehaviourSubject

updateSource(newValue) {
    this._source.next(newValue)
}

Now subscribe in your components to the source

this.service.source.subscribe();

Note the behaviourSubject always needs an initial value and emits the last one

DOCS: https://www.learnrxjs.io/subjects/behaviorsubject.html

If you want to share the data from a httpRequest you should use shareReplay() operator instead, you can subscribe to the httpRequest from different components and the request will be made once and the data will be shared

DOCS: https://www.learnrxjs.io/operators/multicasting/sharereplay.html

julianobrasil · Accepted Answer · 2019-08-07 10:00:59Z

1

There are a few ways to do that. One of them is described here.

1) Build your service like this:

// ReplaySubject is more flexible than BehaviorSubject, as it
// allows you to define how many past emissions should be available.
// But you can get an equivalent code with BehaviorSubject by
// coding like this:
// private _coachProfile$: BehaviorSubject<any | null> = 
//    new BehaviorSubject<any | null>(null);
private _coachProfile$: ReplaySubject<any> = new ReplaySubject<any>(1);

coachProfile(token :string)
{  
  return this.http.post<any>(this.apiURL+'/coach/profile_infos',{
    token: token,
  }).subscribe((profile) => this._coachProfile$.next(profile));        
}

subscribeToGetCoachProfile$()
{  
  return this._coachProfile$.asObservable();       
}

2) And in your components:

ngOnInit() {
  this.coachService.subscribeToGetCoachProfile$()
    .subscribe((profile) => this.coachProfile = profile);
}

Well there are other approaches you can think of, but I think this is the simpler one given the sample code you pasted on your question.

As a side note: if you do some search on stackoverflow, you'll see that this question (or similar questions) has been asked many times here. Take a look, for example in this other approach: Multiple subscriptions without recalculate common part

edited Aug 7, 2019 at 10:00

answered Aug 5, 2019 at 9:12

julianobrasil

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2 Comments

kkD97 Over a year ago

Thanks for your explanation on Replay subject! But I used Behavior Subject instead of it.

Mile Mijatović Over a year ago

@kkD97 , it's the same logic as with BehaviorSubject

Malik M · Accepted Answer · 2019-08-05 09:16:15Z

Here's how to solve your problem using a behavior subject:

@Injectable()
export class CoachService {
  apiURL = environment.apiURL;

  constructor(private http: HttpClient) { }

  updateProfile(info, token, us_id): Observable<any> {
    return Observable.create((behaviorSubject: BehaviorSubject<any>) => {
      const requestData = {
        token: token,
        us_id: us_id,
        us_lang: info.us_lang,
        us_firstname: info.us_firstname,
        us_lastname: info.us_lastname,
        us_sex: info.us_sex,
        us_birthdate: info.us_birthdate,
        us_national_number: info.us_national_number,
        us_email: info.us_email,
        us_gsm: info.us_gsm,
        online_profile: info.online_profile,
        us_address: info.us_address,
        us_zip: info.us_zip,
        us_city: info.us_city,
        country: {
          id: info.country.id
        }
      };
      const url = [this.apiURL, '/coach/update_profile'].join('');

      return this.http.post(url, requestData).subscribe(
        data => {
          behaviorSubject.next(data);
        },
        err => {
          behaviorSubject.error(err);
          if (err && err.status === 401) {
            // Do some err handling
          }
        }
      );
    });
  }

}

Now when you want to post data and subscribe to the result of your Behavior Subject from, say to the in the component you have here, you simply:

 updateCoordonees() {
  this.coachService.updateProfile(this.infos_profile, this.token, this.us_id)
    .subscribe((data: any) => {

      if (data.success && data.msg != null) {
        // do something on success
      }

    },
      (err) => {
        // do some err handling
      });
}

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