模板不使用异步管道呈现可观察的

Question

我刚开始使用 angular，在试图了解自己发生了什么之后，我就是想不出解决方案。我有一个简单的模板：

<div *ngIf="allProducts$ | async as products">
  <div *ngIf="products.size > 0; else noProducts">
    <ul>
      <li *ngFor="let product of products" >
        <span>{{product.id}}</span>
        <span>{{product.name}}</span>
        <span (click)="productDetail(product)">Go to detail</span>
      </li>
    </ul>
  </div>
  <ng-template #noProducts>There are no products yet.</ng-template>
</div>

与 class:

import {Component, OnInit} from '@angular/core';
import {Observable} from 'rxjs';
import {Product} from '../../model/product';
import {Router} from '@angular/router';
import {ProductService} from '../../service/product.service';

@Component({
  selector: 'app-product-list',
  templateUrl: './product-list.component.html',
  styleUrls: ['./product-list.component.css']
})
export class ProductListComponent implements OnInit {

  public allProducts$: Observable<Product[]>;

  constructor(private router: Router,
              private productService: ProductService) {}

  ngOnInit() {
    console.log('constructing ProductListComponent');
    this.allProducts$ = this.productService.getAllProducts();
  }

  productDetail(product: Product) {
    this.router.navigate([`product/${product.id}`]);
  }

}

最后，服务：

import {Injectable} from '@angular/core';
import {HttpClient} from '@angular/common/http';
import {API_URL} from '../../app.constants';
import {Product} from '../model/product';
import {first, map} from 'rxjs/operators';
import {BehaviorSubject, Observable} from 'rxjs';

@Injectable({
  providedIn: 'root'
})
export class ProductService {

  constructor(private http: HttpClient) {
  }

  addProduct(product: Product) {
    return this.http.post<Product>(`${API_URL}/product`, product, {observe: 'response'});
  }

  getAllProducts(): Observable<Product[]> {
    return this.http.get<Product[]>(`${API_URL}/product`, {observe: 'response'})
      .pipe(map(response => response.body), first());
  }
}

很简单的东西。我只是无法让它呈现。所以我尝试在服务中创建一个行为主题并将其订阅到http observable，并将其返回给组件而不是原始的http observable，认为可能组件没有机会及时订阅，如this中所述。没有运气。

接下来，受 this SO question 的启发，我尝试在订阅中手动调用 markForCheck，完全删除异步管道。再一次，什么都没有。

我找不到任何其他解决方案，但这两个是最常见的方法，而且它似乎在任何地方都有效，比如 here or here. Why doesn't it work for me? Clearly, there is something simple eluding me. When I log the response body in the console in the subscription lambda, I can see the product entities I expect from backend, but neither async pipe or subscription in ngOnInit work. I have also seen an approach using ，但我觉得可以简单地完成同样的事情作为常规订阅和 markForCheck。

Answer 1

这看起来不对...

<div *ngIf="products.size > 0; else noProducts">

你的意思是：

<div *ngIf="products.length > 0; else noProducts">

模板不使用异步管道呈现可观察的

Template does not render observable using async pipe

angular2-observables

angular