如何防止 RxJs observable 完成错误？

Question

我有一个 angular reactive form that makes a simple GET request. If for example, I should get some sort of HTTP error. The observable todo$ has now completed I can no longer change my search options and click to retry searching. I've made a stackblitz demo，在演示中，我在初始化程序中添加了我的订阅，如果流中有错误，我会捕获它。在我抓住它之后，我再次调用初始化程序。这可行，但似乎是处理错误的错误方法。

我已经设置了表单，以便我可以取消以前的 HTTP 请求。

export class AppComponent implements OnDestroy {
  todos;
  loading = false;
  useFakeURL = false;
  todoSub$: Subscription;
  todo$: BehaviorSubject < string > = new BehaviorSubject < string > ('');

  @ViewChild('searchInput') searchInput: ElementRef;

  constructor(private provider: ExampleService) {
    this.init();
  }

  ngOnDestroy() {
    this.todoSub$.unsubscribe();
  }

  search() {
    const value = this.searchInput.nativeElement.value;
    this.todo$.next(value);
    this.useFakeURL = !this.useFakeURL;
  }

  private init(): void {
    this.todoSub$ = this.todo$.pipe(
        filter(val => !!val),
        tap(() => {
          this.loading = true;
        }),
        switchMap(() => this.provider.query(this.todo$.getValue(), this.useFakeURL)),
        catchError(error => {
          this.todo$.next('');
          this.init();
          return of([]);
        }),
      )
      .subscribe(
        todos => {
          this.loading = false;
          this.todos = todos;
        },
        err => {
          this.loading = false;
          this.todos = err;
        }
      );
  }
}

export class ExampleService {

  constructor(private http: HttpClient) {}

  query(todo, useFakeURL: boolean) {
    if (todo === 'all') {
      todo = '';
    }
    const url = useFakeURL ? 'poop' : `https://jsonplaceholder.typicode.com/todos/${todo}`;
    return this.http.get(url);
  }
}

<div class="container">
  <input #searchInput type="text" placeholder="Enter a number or enter 'all' to get all todos">
  <button (click)="search()">Get Todos</button>
</div>
<ul *ngIf="!loading && todos && todos.length">
  <li *ngFor="let todo of todos">
    <pre>
      {{todo | json}}
    </pre>
  </li>
</ul>
<pre *ngIf="!loading && todos && !todos.length">
  {{todos | json}}
</pre>
<div *ngIf="loading" class="loader">... LOADING</div>

Answer 1

Angular 的 Http 请求是不可变的。当您订阅它时，从客户端返回的 Observable 会执行实际调用。您订阅多少次，就会收到多少次请求。也就是所谓的"Cold Observable"

如果您需要更改请求，您需要一个全新的来自 HttpClient 的可观察对象。

Answer 2

正如@kos 所提到的，我在错误的地方发现了错误。由于我切换到一个新的可观察对象，我应该在 switchMap 中捕获错误。 UPDATED-DEMO

search(term: Observable < string > ) {
  return term.pipe(
    filter(val => !!val),
    distinctUntilChanged(),
    debounceTime(500),
    // attached catchError to the inner observable here.
    switchMap(term => this.searchTodo(term).pipe(catchError(() => {
      return of({
        error: 'no todo found'
      });
    }))),
  );
}

如何防止 RxJs observable 完成错误？

How to keep RxJs observable from completing on error?

rxjs

angular

angular-reactive-forms