将 Angular 中共享服务的属性用作 getter 和 setter 的私有属性的原因是什么？

Question

In all the manuals shared service for passing data between the angular components should seem like below.

What is a reason to use properties of shared service in Angular as private with getters and setters?

@Injectable()
class SharedService {
  private someValue$ = new BehaviorSubject<SomeType>(null);

  public getSomeValue(): BehaviorSubject<SomeType> {
    return this.someValue$;
  }

  public setSomeValue(someValue: SomeType): void {
    this.someValue$.next(someValue);
  }
}

Answer 1

The example you show is not the complete picture for a shared services pattern, although it comes close.

You normally don't pass the Subject but an Observable that comes from that Subject. This prevents others from directly sending info to all subscribers, but always via the Service. In that way you can filter etc what is send.

@Injectable()
class SharedService {
  private someValueSubj = new BehaviorSubject<SomeType>(null);
  someValue$ = this.someValueSubj.asObservable();

  public getSomeValue(): Observable<SomeType> {
    return this.someValue$;
  }

  public setSomeValue(someValue: SomeType): void {
    this.someValueSubj.next(someValue);
  }
}

Furthermore this pattern is extended by having methods in the service that do something with the result being send through the Subject:

@Injectable()
class SharedService {
  private someValueSubj = new BehaviorSubject<SomeType>(null);
  someValue$ = this.someValueSubj.asObservable();

  public getSomeValue(): Observable<SomeType> {
    return this.someValue$;
  }

  private setSomeValue(someValue: SomeType): void {
    this.someValueSubj.next(someValue);
  }

  public doSomethingServiceLike():void{
      this.setSomeValue(someType);
  }
}

In this way the service can do its' "thing" and all subscribers get the result of that.

I hope this helps.