Angular observables - 如果没有订阅，我是否需要取消订阅？

Question

我正在使用最新的 angular 8，并且对 observables 的概念很陌生。我的问题是，如果我直接调用一个 observable 而不是将其应用于订阅变量，我是否还需要取消订阅。以下是我想知道是否需要取消订阅的情况？
提前谢谢了

场景 1 - 从组件调用 httpService:

Service - httpService

     getContactsHttp(){
         let headers: any = new HttpHeaders(this.authService.getHeadersClient());
         return this.httpClient.get('/contacts', {headers: headers})
          .pipe(timeout(this.authService.getTimeoutLimit('normal')));
        }

Component - Calling getContactsHttp and sorting response

getContacts() {
 this.httpService.getContactsHttp().subscribe((data:any[])=>{
  this.records = this.sortData(data)
 })
}

场景 2 - 在组件中订阅的 observable

contacts$: new Subject<any[]>;

ngOnInit() {
  this.getContacts();
  this.contacts$.subscribe((data:any[])=>{
    this.records = this.sortData(data);
  })
}

getContacts() {
    this.httpService.getContactsHttp().subscribe((data:ContactSearch[])=>{      
      this.contacts$.next(data);
    })
  }

服务 - httpService

     getContactsHttp(){
         let headers: any = new HttpHeaders(this.authService.getHeadersClient());
         return this.httpClient.get('/contacts', {headers: headers})
          .pipe(timeout(this.authService.getTimeoutLimit('normal')));
        }

Answer 1

简短的回答，是的，您仍然将组件中的 observable 取消订阅 avoid subscription leaks 。我的首选方法之一是使用 takeUntil() 运算符。

这就是您可以在组件中使用它的方式。

private unsubscribe: Subject<void> = new Subject();

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

getContacts() {
  this.httpService.getContactsHttp()
    .pipe(
      takeUntil(this.unsubscribe),
    ).subscribe((data:ContactSearch[])=>{      
      this.contacts$.next(data);
    });
 }

正如 Brian Love 所解释的，

• First, we import the takeUntil() operator as well as the Subject class.
• Next, we define a private instance property named unsubscribe, which is a Subject.
• We also create a new instance of Subject, defining the generic type as void. We use the takeUntil() operator in the pipe() method before invoking subscribe(), providing the unsubscribe observable.
• In the ngOnDestroy() lifecycle method we emit a next() notification, and then complete() the unsubscribe observable. The subscription is now complete, and we have immediately unsubscribed when the ngOnDestroy() method is invoked during the lifecycle of our component.