无法使用Observable更新Angular 2中的列表

<ul>
  <li *ngFor="let item of items$ | async">{{ item }}</li>
</ul>

items$: Observable<any[]>;

ngOnInit() {
  this.items$ = this.dataService.getItems();
}

import { Subject } from 'rxjs';

private itemsSubject = new Subject<any[]>();
items$ = this.itemsSubject.asObservable();

updateItems(newItems: any[]) {
  this.itemsSubject.next(newItems);
}

updateList() {
  this.dataService.updateItems(newItems);
}

import { switchMap } from 'rxjs/operators';

getItems(): Observable<any[]> {
  return this.http.get<any[]>('api/items').pipe(
    switchMap(response => {
      // 处理获取到的数据
      return this.processData(response);
    })
  );
}

private processData(response: any[]): Observable<any[]> {
  // 处理数据逻辑
  return of(processedData);
}