Angularjs 带有异步管道的Angular*ngfor在api post请求后不更新DOM

offers$observable通过异步管道和*ngfor推送到子组件。当它通过post请求更新时，更改不会在DOM中呈现。如果我使用一个数组并订阅获取请求，而不是使用异步管道并通过异步管道进行观察，它就会工作……不知道为什么

App Component.ts

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.scss'],
})
export class AppComponent {
  title = 'promoapp';

  offers$:Observable<Offer[]>

  constructor(private offerservices : OffersService){}

  ngOnInit(): void {
    this.offers$ = this.offerservices.loadOffers()
  }

  onOfferSubmitted(offer:Offer){
    this.offerservices.PostRequest(offer);
    this.offers$ = this.offerservices.loadOffers()

  }
}

---

感谢

我通过修改onOfferSubmitted方法并订阅post请求，解决了这个问题

  onOfferSubmitted(offer:Offer){
    this.offerservices.PostRequest(offer).subscribe(()=>{
      this.offers$=this.offerservices.loadOffers()
    })

@Component({
  selector: 'app-offerdisplay',
  templateUrl: './offerdisplay.component.html',
  styleUrls: ['./offerdisplay.component.scss'],
})
export class OfferdisplayComponent implements OnInit {

  @Input()
  offer:Offer
  
  
  constructor() { }

  ngOnInit(): void {

  }

}

  onOfferSubmitted(offer:Offer){
    this.offerservices.PostRequest(offer).subscribe(()=>{
      this.offers$=this.offerservices.loadOffers()
    })