angular - Rxjs 获取不到过去的值

Question

我正在尝试获取发出的最后 3 个值，使用下面的代码我期望在填充 uiOrder 并调用 cancelOrderItem() 几次后，我可以使用 getHistory() 访问订单的最后 3 个修订，但是我实际上得到了最后一个(当前)值 3 次，我尝试过 replaySubject(3) 得到相同的结果。这是我的代码:

export class OrdersService {

  public readonly orders: Observable<Order[]>;
  public readonly uiOrder: Observable<Order>;

  private _orders: BehaviorSubject<Order[]>;
  private _uiOrder: BehaviorSubject<Order>;

  private dataStore: {
    uiOrder: Order,
    orders: Order[]
 };


  constructor() {

    this.dataStore = {
      uiOrder: null,
      orders: []
    };

    this._orders = <BehaviorSubject<Order[]>>new BehaviorSubject([]);
    this._uiOrder = <BehaviorSubject<Order>>new BehaviorSubject({});
    this.orders = this._orders.asObservable();
    this.uiOrder = this._uiOrder.asObservable();
  }

  getOrder(orderId: number | string) {
    for (let i = 0; i < this.dataStore.orders.length; i++) {
      if (this.dataStore.orders[i].id == orderId) {
        this.dataStore.orders[i].lastAccess = moment().format().slice(0, 19) + 'Z';
        this.dataStore.uiOrder = this.dataStore.orders[i];
        this.updateUiOrder();
      }
    }
  }


  cancelOrderItem(action) {
    this.dataStore.uiOrder.sections[action.sectionIndex].orderDetails.splice(action.orderDetailsIndex, 1);
    this.updateUiOrder()
  }

  getHistory() {
    this.uiOrder.take(3).subscribe((res) => {
      console.log('uiOrder', res);
    }).unsubscribe()
  }

  updateUiOrder() {
    console.log('updating ui order');
    this._uiOrder.next(this.dataStore.uiOrder);
  }

}

我做错了什么？

Answer 1

您要找的接线员是bufferCount(3,1)它创建了一个包含最后 3 个值的滑动窗口。缺点:它只会在累积 3 个值后才开始发射。如果你想获得第一个值，你可以这样做:

Rx.Observable.from([null,null])
  .concat(this.uiOrder)
  .bufferCount(3,1)
  .subscribe(uiOrderHistory => ... );

这样您的弹珠图将如下所示:

---Order1-----------------Order2--------------------Order3
bufferCount(3,1)
---[null,null,Order1]-----[null,Order1,Order2]------[Order1,Order2,Order3]