如何修复“无法读取未定义的属性"标题" [英] How to fix "Cannot read property 'title' of undefined"

问题描述

我正在关注Mosh Hamedani教程"Angular 4:Pro的初学者".

I'm following Mosh Hamedani tutorial "Angular 4: Beginner to Pro".

我试图在编辑产品时以表格形式显示产品标题.产品存储在Firebase数据库中.我是Angular的新手.

I'm trying to show the title of a product in a form when trying to edit it. The product is stored in a firebase database. I'm new to Angular.

但是，当我进入编辑表单时，在控制台中出现此错误

However, I'm getting this error in the console when I go to the edit form

ERROR TypeError: Cannot read property 'title' of undefined
    at Object.eval [as updateDirectives] (ProductFormComponent.html:7)
    at Object.debugUpdateDirectives [as updateDirectives] (core.js:23911)
    at checkAndUpdateView (core.js:23307)
    at callViewAction (core.js:23548)
    at execComponentViewsAction (core.js:23490)
    at checkAndUpdateView (core.js:23313)
    at callViewAction (core.js:23548)
    at execEmbeddedViewsAction (core.js:23511)
    at checkAndUpdateView (core.js:23308)
    at callViewAction (core.js:23548)

这是我表格的一部分:

<div class="form-group">
            <label for="title">Title</label>
            <input #title="ngModel" [(ngModel)]="product.title" <== error here
name="title" id="title" type="text" class="form-control" required>
            <div class="alert alert-danger" *ngIf="title.touched && title.invalid">
              Title is required
            </div>
          </div>

这是product-form.component.ts

And here is the product-form.component.ts

import { Component, OnInit, OnDestroy } from '@angular/core';
import { CategoryService } from 'src/app/category.service';
import { ProductService } from 'src/app/product.service';
import { Router, ActivatedRoute } from '@angular/router';
import { take } from 'rxjs/operators';

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

  categories$;
  product;

  constructor(
    categoryService: CategoryService,
    private route: ActivatedRoute,
    private productService: ProductService,
    private router: Router) {
    this.categories$ = categoryService.getCategories();

    let id = this.route.snapshot.paramMap.get('id');
     if (id) this.productService.get(id).snapshotChanges().pipe(take(1))
.subscribe(p => this.product = p); <== this does not seem to be working
  }

  save(product) {
    this.productService.create(product);
    this.router.navigate(["/admin/products"]);
  }

  ngOnInit() {
  }

}

我该怎么做才能显示产品标题?

What can I do to show the product's title?

推荐答案

更改

product;

到

product:any = {};

和(valueChanges()而不是snapshotChnages())

and (valueChanges() instead of snapshotChnages())

if (id) this.productService.get(id).snapshotChanges().pipe(take(1))
.subscribe(p => this.product = p); 
  }

到

if (id) this.productService.get(id).valueChanges().pipe(take(1))
.subscribe(p => this.product = p); <== this does not seem to be working
  }

已解决问题

这篇关于如何修复“无法读取未定义的属性"标题"的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！