Angular 5：错误类型错误：无法读取未定义的属性“偏移量”

Question

错误： ERROR TypeError: Cannot read property 'offset' of undefined

我有漫画组件，工作正常，但我决定制作一个子组件，现在它不工作了。 我有一个父组件“漫画”和一个子组件“分页”。漫画显示正常，但分页不工作。

在代码中，console.log(this.pagination); 返回一个类似 ('offset': 20, 'count':1) 的数组

但是 pagination.component.html ir 返回错误 Cannot read property 'offset' of undefined 所以分页是空的，没有数据。所以父漫画.component.ts 不会与子共享这个变量。

我尝试在 pagination.component.ts 中声明 pagination: Pagination;，但 pagination 仍然是空的。

所以我认为我以错误的方式声明了某些内容，或者我应该声明一些我没有声明的内容。我进行了搜索，并试图找到丢失的内容，但没有找到任何内容，并且仍然无法正常工作。

我的代码：

// file: pagination.ts

export class Pagination {
  offset: number;
  count: number;
}



// file: /comics/comics.component.ts

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute, Params } from '@angular/router';

import { Comic } from '../comic';
import { Pagination } from '../pagination';
import { ComicService } from '../comic.service';

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

  comics: Comic;
  pagination: Pagination;

  constructor(
    private route: ActivatedRoute,
    private comicService: ComicService
  ) {}

  ngOnInit() {
  }

  getComics(): void {
    const offset = +this.route.snapshot.paramMap.get('offset');
    this.comicService.getComics(offset, 20)
    .subscribe(
      result => {
        this.comics = result['data']['results'];
        console.log(this.comics);

        this.pagination.offset = result['data']['offset'];
        this.pagination.count = result['data']['count'];

        console.log(this.pagination);
  }
);
  }
}


// file: /pagination/pagination.component.ts

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute, Params } from '@angular/router';

import { Pagination } from '../pagination';

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

  constructor() { }

  ngOnInit() {
  }

}


// file: comics/comics.component.html

<div *ngFor="let comic of comics">
  <h5>{{comic.title | uppercase}} </h5>
</div>

<app-pagination></app-pagination>



// file: pagination/pagination.component.html

<div>
  <h5>{{pagination.offset}}</h5>
  <span>{{pagination.count}}</span>
</div>

使用的版本：

Angular CLI：1.7.3

节点：8.9.4

操作系统：darwin x64

角度：5.2.8

Answer 1

鉴于这两个组件处于父子关系，您最好的选择是简单地将offset 和count 定义为子组件的输入属性，并从父组件传递它们，如下所示：

comics.component.ts

import { Component, OnInit } from '@angular/core';
import { ActivatedRoute, Params } from '@angular/router';

import { Comic } from '../comic';
import { Pagination } from '../pagination';
import { ComicService } from '../comic.service';

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

  comics: Comic;
  offset;
  count;

  constructor(
    private route: ActivatedRoute,
    private comicService: ComicService
  ) {}

  ngOnInit() {
  }

  getComics(): void {
    const offset = +this.route.snapshot.paramMap.get('offset');
    this.comicService.getComics(offset, 20)
    .subscribe(
      result => {
        this.comics = result['data']['results'];
        console.log(this.comics);

        this.offset = result['data']['offset'];
        this.count = result['data']['count'];
  }
);
  }
}

pagination.component.ts

import { Component, OnInit, Input } from '@angular/core';
import { ActivatedRoute, Params } from '@angular/router';

import { Pagination } from '../pagination';

@Component({
  selector: 'app-pagination',
  templateUrl: './pagination.component.html',
  styleUrls: ['./pagination.component.css']
})
export class PaginationComponent implements OnInit {
  @Input() offset;
  @Input() count;
  constructor() { }

  ngOnInit() {
  }

}

comics.component.html

<div *ngFor="let comic of comics">
  <h5>{{comic.title | uppercase}} </h5>
</div>

<app-pagination [offset]="offset" [count]="count"></app-pagination>

pagination.component.html

<div>
  <h5>{{offset}}</h5>
  <span>{{count}}</span>
</div>