如何在 Angular 7 中创建延迟加载树视图

Question

我正在使用 Angular 创建一个 TreeView 创建 treeview 的场景是我对每个级别都有不同的 API 意味着如果我单击其中一个父级别节点，那么只有子节点应该只为该特定节点生成，依此类推进一步级别和每个子节点列表来自 API

现在的问题是，当我在创建的树视图中创建嵌套列表时，单击任何节点。正在为该节点和其他节点生成子节点。

这是我的代码。

<ul>
    <li *ngFor="let item of companyList" [id]="item.id">
        <span (click)="getLocation(item)">{{item.description}}</span>
      <ul>
          <li *ngFor="let loc of loactionData" [id]="loc.id">
          <span (click)="getDepartment(loc)">{{loc.description}}</span>
          <ul>
            <li *ngFor="let depart of deaprtmentData">
              <span (click)="getEmpStatus(depart)">{{depart.description}}</span>
            </li>
           </ul>
          </li>
    </ul>
  </li>
</ul>

注意：每个列表都来自单独的 API，这些点击事件有助于调用 API。

请帮助我解决上述问题，在此先感谢。

Answer 1

您可以通过列表中父项的索引来跟踪不同的数据集（例如，如果某个项目从列表中删除并且索引发生变化，则首选 id）

public locationData = {};

load locationData(item, index):

this.locationData[index] = getDataForItem(item);

.....

<ul>
            <li *ngFor="let item of companyList; let companyIndex = index;" [id]="item.id">
              <span (click)="getLocation(item, companyIndex)">{{item.description}}</span>
              <ul>
                <li *ngFor="let loc of loactionData[companyIndex]; let locationIndex = index;" [id]="loc.id">
                  <span (click)="getDepartment(loc, locationIndex)">{{loc.description}}</span>
                  <ul>
                    <li *ngFor="let depart of deaprtmentData[locationIndex]; let departmentIndex = index;">
                      <span (click)="getEmpStatus(depart, departmentIndex)">{{depart.description}}</span>

                    </li>
                  </ul>
                </li>
              </ul>
            </li>
          </ul>

Answer 2

您正在为每个嵌套 ul 重复相同的嵌套列表。您必须将嵌套列表与其父项相关联。

由于您的 companyList 项目和您的 locationData 项目有一个 ID，使用这个 ID 将嵌套列表关联到每个公司和每个位置。

要进行关联，请使用一个简单的对象在您的代码中创建一个地图，并使用索引签名键入它。在您的情况下，它看起来像这样：

companyList: Company[] = [];
locationData: { [companyId: string]: Location[] } = {};
departmentData: { [locationId: string]: Department[] } = {};

然后在您的模板中，您需要使用 item.id 和 loc.id:

索引 locationData 和 departmentData

<ul>
  <li *ngFor="let item of companyList" [id]="item.id">
    <span (click)="getLocation(item)">{{ item.description }}</span>
    <ul>
      <li *ngFor="let loc of locationData[item.id]" [id]="loc.id">
        <span (click)="getDepartment(loc)">{{ loc.description }}</span>
        <ul>
          <li *ngFor="let depart of departmentData[loc.id]">
            <span (click)="getEmpStatus(depart)">{{ depart.description }}</span>
          </li>
        </ul>
      </li>
    </ul>
  </li>
</ul>

生成数据时，将其放在对象中正确的 ID 下：

getLocation(item: Company): void {
  this.http.get<Location[]>(`${this.api}/locations?companyId=${item.id}`).subscribe(locations => {
    this.locationData[item.id] = locations;
  })
}

getDepartment(location: Location): void {
  this.http.get<Department[]>(`${this.api}/departments?locationId=${location.id}`).subscribe(departments => {
    this.departmentData[location.id] = departments;
  })
}

Here is an example with a User/Post/Comment data model and the jsonplaceholder API.

See this Stackblitz demo for a live example

<ul>
  <li *ngFor="let user of users" [id]="user.id">
    <span (click)="getPosts(user)">{{ user.name }}</span>
    <ul>
      <li *ngFor="let post of posts[user.id]" [id]="post.id">
        <span (click)="getComments(post)">{{ post.title }}</span>
        <ul>
          <li *ngFor="let comment of comments[post.id]">
            <span>{{ comment.name }}</span>
          </li>
        </ul>
      </li>
    </ul>
  </li>
</ul>

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable, of } from 'rxjs';

interface User {
  id: number;
  name: string;
  username: string;
  email: string;
}

interface Post {
  userId: number;
  id: number;
  title: string;
  body: string;
}

interface Comment {
  postId: number;
  id: number;
  name: string;
  email: string;
  body: string;
}

@Component({
  selector: 'my-app',
  templateUrl: './app.component.html',
  styleUrls: [ './app.component.css' ]
})
export class AppComponent implements OnInit {
  users: User[] = [];
  posts: { [id: number]: Post[] } = {};
  comments: { [id: number]: Comment[] } = {};

  private api = 'https://jsonplaceholder.typicode.com';

  constructor(private http: HttpClient) { }

  ngOnInit(): void {
    this.http.get<User[]>(`${this.api}/users`).subscribe(users => this.users = users);
  }

  getPosts(user: User): void {
    this.http.get<Post[]>(`${this.api}/posts?userId=${user.id}`).subscribe(posts => {
      this.posts[user.id] = posts;
    })
  }

  getComments(post: Post): void {
    this.http.get<Comment[]>(`${this.api}/comments?postId=${post.id}`).subscribe(comments => {
      this.comments[post.id] = comments;
    })
  }
}

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