angular - RxJS : Filter one observable using another observable

Question

我有一个流携带来自 API 响应的数据，另一个流发出需要从源流中过滤的值。

@Injectable({
    providedIn: 'root'
})
export class SmpService {
    private _smp$ = new ReplaySubject(1);
    private _deleteSubject = new BehaviorSubject(null);

    constructor(private http: HttpClient) {
        const allSmp$ = this.loadSmp().pipe(map(list => list.map(item => item.id)));
        const delete$ = this._deleteSubject.pipe(map(value => this.filterSmp(value)));

        allSmp$
            .pipe(
                combineLatest(delete$, (notifications, xf) => {
                    return xf(notifications);
                }),
                tap(x => console.log('console ', x))
            )
            .subscribe(this._smp$);
    }

    loadSmp(): Observable<any> {
        const contextPath = 'some_url';
        const url = this.uriPrefix + contextPath;
        return this.http.get(url).pipe(map((response: any) => response.notifications || []));
    }

    filterSmp(value) {
        return notifications => notifications.filter(notification => value !== notification);
    }

    deleteSmp(subscribeItem) {
        this._deleteSubject.next(subscribeItem);
    }

    getSmp(): Observable<any> {
        return this._smp$.asObservable();
    }
}

过滤正常。但是在页面加载时，我无法获得在页面上呈现的初始 API 响应。只有当我通过某些操作触发 deleteStream 时，我才会收到它。

有什么方法可以在没有触发 deleteStream 的情况下获取初始数据？

Answer 1

使用带有一些默认值的 BehaviorSubject 而不是 Subject。例如 null。

private _deleteSubject = new BehaviorSubject(null);

BehaviorSubject 每次订阅时都会发出默认值。