html - Angular product-details.component.html 对象可能是 'undefined'

Question

我正在关注 View Product Details angular网站上的教程，遇到错误:

Error in src/app/product-details/product-details.component.html (4:16) Object is possibly 'undefined'.

我无法继续下一个教程，因为它需要此页面才能运行。

代码如下:

product-list.component.html

<h2>Products</h2>

<div *ngFor="let product of products">

<h3>
  <a [title]="product.name + ' details'" [routerLink]="['/products', product.id]">
    {{ product.name }}
  </a>
</h3>   
</div>

product-details.component.ts

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute } from '@angular/router';
import { Product, products } from '../products';
@Component({
  selector: 'app-product-details',
  templateUrl: './product-details.component.html',
  styleUrls: ['./product-details.component.css']
})

export class ProductDetailsComponent implements OnInit {
  product: Product|undefined;
  constructor(
    private route: ActivatedRoute,
  ) { }

  ngOnInit() {
    // First get the product id from the current route.
    const routeParams = this.route.snapshot.paramMap;
    const productIdFromRoute = Number(routeParams.get('productId'));

    // Find the product that correspond with the id provided in route.
    this.product = products.find(product => product.id === productIdFromRoute);
  }

}

product-details.component.html

<h2>Product Details</h2>

<div *ngIf="product">
<h3>{{ product.name }}</h3>
<h4>{{ product.price | currency }}</h4>
<p>{{ product.description }}</p>

</div>

我希望有人可以帮助解决问题，因为我看到代码正在运行。

谢谢。

Answer 1

我也在做这个教程，我通过将 ProductDetailsComponent 添加到 app.module.ts 中的声明来修复它。

declarations: [
AppComponent,
TopBarComponent,
ProductListComponent,
ProductAlertsComponent,
ProductDetailsComponent //<-- add this into declarations
],

别忘了先在 app.module.ts 中导入 ProductDetailsComponent。

import { ProductDetailsComponent } from './product-details/product-details.component';

刷新整个网站后它应该可以工作(不仅仅是右侧的显示，去保存并刷新浏览器选项卡)。