javascript - Angular2 Observable 不是由异步管道触发的

Question

考虑 angular2/rxjs/typescript 的这个简单片段

  public rooms: Observable<Room[]>;      

  constructor ( ... ) {

    this.rooms = this.inspectShipSubject
      .do(() => console.log('foo'))
      .switchMap(ship => this.roomByShipService.getRoomsByShip(ship));

    //this.rooms.subscribe(); // <-- [1]
  }

这是模板:

<some-component *ngFor="let room of rooms | async" [room]="room"></some-component>

除非我取消注释 [1] 指示的行，否则它不起作用('foo' 未打印且无数据显示)。为什么模板不触发可观察对象自动执行？

有没有比使用空白订阅更好的方法？

Answer 1

好吧，我不确定为什么，但诀窍是在 this.inspectShipSubject 上使用 BehaviourSubject 而不是 Subject。

这很好用，并由模板正确触发。

  public rooms$: Observable<Room[]>;

  private inspectShipSubject: BehaviorSubject<Ship> = new BehaviorSubject<Ship>(null);

  constructor(
    ...
  ) { }

  ngOnInit() {
    this.rooms$ = this.inspectShipSubject.switchMap(ship => this.roomByShipService.getRoomsByShip(ship));
  }

  @Input()
  set ship(ship: Ship) {
    this.inspectShipSubject.next(ship);
  }

  get ship(): Ship {
    return this.inspectShipSubject.getValue();
  }

和模板:

<some-component *ngFor="let room of (rooms | async)" [room]="room"></some-component>