循环通过可观察数组并更新计算值

Question

我有一个Observable数组，我希望能够拥有一个包含来自数组内容的计算值的公共值。

@Injectable()
export class PaymentsProvider {

  total: number = 0;

  private payments = new BehaviorSubject(<Payment[]>[]);
  payments$: Observable<Payment[]> = this.payments.asObservable();

  constructor() {

    console.log("init payments service")
    this.total = 0
    this.payments$.subscribe( payments => {
       for (let payment of payments) {
         this.total += payment.amount
       }
    })    
  }
}

这样做，我可以从其他组件调用this.paymentsService.total，但是如果我离开页面组件并导航回来，则值加倍，即使payments数组有没有改变。

我应该以不同的方式计算这个吗？

Answer 1

将this.total = 0;放入您订阅的回调

中

＆＃13;

＆＃13;

    
    this.payments$.subscribe( payments => {
       this.total = 0
       for (let payment of payments) {
         this.total += payment.amount
       }
    })    

＆＃13;

＆＃13;

＆＃13;