javascript - 当使用 rxjs 6 以 Angular 6 发出新请求时如何取消正在进行的 HTTP 请求

Question

我的应用程序中有两个 HTTP 服务 RxnsSearchService 和 RxnsSearchHitCountService。

使用 forkJoin 处理两个请求，如下面的代码。

constructor(
  private rxnsSearchService: RxnsSearchService,
  private rxnsSearchHitCountService: RxnsSearchHitCountService
) { }
const rxnsObservable: Observable<Array<any>> = this.rxnsSearchService.getReactions(this.searchParams, filters);
const headCountObservable: Observable<number> = this.rxnsSearchHitCountService.getHitCount(this.searchParams, filters);
forkJoin([rxnsObservable, headCountObservable]).pipe().subscribe((results) => { //handling results 
},
  error => {
    console.log(error);
  });

每当有新请求到来时，我想取消正在进行的旧请求。谁能帮我解决这个问题？

export class RxnsSearchService {
  sub: Subject<any> = new Subject();
  constructor(private httpClient: HttpClient) {}

  getReactions(params: Params, offset: number, perPage: number, filters: any) {
    const body = {
      filters: filters,
      query: params.query
    };
     return this.httpClient.post(environment.rxnsSearch, body).pipe(
      map((response: Array<any>) => {
        return response;
      }),
      catchError(error => {
        console.log(error);
        return throwError(error);
      })
    );
  }
}

export class RxnsSearchHitCountService {
  constructor(private httpClient: HttpClient) {}

  getHitCount(params: Params, filters: any) {
    const body = {
      filters: filters,
      query: params.query,
    };
    return this.httpClient.post(environment.rxnsSearchHitCount, body).pipe(
      map((response: number) => {
        return response;
      }),
      catchError(error => {
        console.log(error);
        return throwError(error);
      })
    );
  }
}

Answer 1

我将通过一个简化的示例来介绍如何执行此操作的一般方法。假设我们目前有这个:

public getReactions() {
  this.http.get(…)
    .subscribe(reactions => this.reactions = reactions);
}

确保取消旧请求的方法是改为在某些主题上发出:

private reactionsTrigger$ = new Subject<void>();

public getReactions() {
  this.reactionsTrigger$.next();
}

现在我们有一个表示触发新请求的事件流的可观察对象。您现在可以将 OnInit 实现为如下所示:

public ngOnInit() {
  this.reactionsTrigger$.pipe(
    // Use this line if you want to load reactions once initially
    // Otherwise, just remove it
    startWith(undefined),

    // We switchMap the trigger stream to the request
    // Due to how switchMap works, if a previous request is still
    // running, it will be cancelled.
    switchMap(() => this.http.get(…)),

    // We have to remember to ensure that we'll unsubscribe from
    // this when the component is destroyed
    takeUntil(this.destroy$),
  ).subscribe(reactions => this.reactions = reactions);
}

// Just in case you're unfamiliar with it, this is how you create
// an observable for when the component is destroyed. This helps
// us to unsubscribe properly in the code above
private destroy$ = new Subject<void>();
public ngOnDestroy() {
  this.destroy$.next();
  this.destroy$.complete();
}

---

线

    switchMap(() => this.http.get(…)),

在您的情况下，实际上可能会将事件切换到 forkJoin:

    switchMap(() => forkJoin([rxnsObservable, headCountObservable])),

如果您希望单个事件流重新触发两个请求。