如何嵌套ngfor表。只能显示一个嵌套属性

Question

如果在第二个ngFor中我只使用了subtask.taskID，那么一切正常。第二个我包括要插值的第二个东西，即subtask.taskName，它会中断。

如果我注释掉subtask.taskID并保留subtask.taskName，那么一切正常。为什么会这样呢？为什么我的第二个ngFor中无法显示多个子任务？

编辑：类似的问题。无法显示我的子任务的其他属性。我只能得到一个显示。我还更新了代码，因为我正在慢慢处理这个树形网格组件。 stackblitz：https://stackblitz.com/edit/angular-xk9nw6

<H1>Table</H1>

<table  class="table">
  <thead>
  <tr>
    <th>expand</th>
    <th>task id</th>
    <th>task name</th>
    <th>button</th>
  </tr>
</thead>  
<tbody *ngFor="let datum of data">
  <tr>
    <td class="" (click)="subtask(datum)">> </td>
    <td class="">{{datum.taskID}}</td>
    <td class="">{{datum.taskName}}</td>
    <td class="btn btn.primary" (click)="dropdown(datum)">...</td>
  </tr>
      <tr [hidden]="!foo" *ngFor="let subtask of datum.subtasks" >
          <td class="">> </td>
          <td class="">{{subtask?.taskID}}</td>
          <td class="">{{substask?.taskName}}</td>
          <td class=" btn btn.primary" (click)="dropdown(subtask)">...</td>
        </tr>
</tbody>  
 </table>

样本数据

/**
 * Test cases data source
 */
export let sampleData: Object[] = [
    {
        taskID: 1,
        taskName: 'Planning',
        startDate: new Date('02/03/2017'),
        endDate: new Date('02/07/2017'),
        progress: 100,
        duration: 5,
        priority: 'Normal',
        approved: false,
        isInExpandState: true,
        subtasks: [
            { taskID: 2, taskName: 'Plan timeline', startDate: new Date('02/03/2017'), endDate: new Date('02/07/2017'), duration: 5, progress: 100, priority: 'Normal', approved: false },
            { taskID: 3, taskName: 'Plan budget', startDate: new Date('02/03/2017'), endDate: new Date('02/07/2017'), duration: 5, progress: 100, approved: true },
            { taskID: 4, taskName: 'Allocate resources', startDate: new Date('02/03/2017'), endDate: new Date('02/07/2017'), duration: 5, progress: 100, priority: 'Critical', approved: false },
            { taskID: 5, taskName: 'Planning complete', startDate: new Date('02/07/2017'), endDate: new Date('02/07/2017'), duration: 0, progress: 0, priority: 'Low', approved: true }
        ]
    },
    {
        taskID: 6,
        taskName: 'Design',
        startDate: new Date('02/10/2017'),
        endDate: new Date('02/14/2017'),
        duration: 3,
        progress: 86,
        priority: 'High',
        isInExpandState: false,
        approved: false,
        subtasks: [
            { taskID: 7, taskName: 'Software Specification', startDate: new Date('02/10/2017'), endDate: new Date('02/12/2017'), duration: 3, progress: 60, priority: 'Normal', approved: false },
            { taskID: 8, taskName: 'Develop prototype', startDate: new Date('02/10/2017'), endDate: new Date('02/12/2017'), duration: 3, progress: 100, priority: 'Critical', approved: false },
            { taskID: 9, taskName: 'Get approval from customer', startDate: new Date('02/13/2017'), endDate: new Date('02/14/2017'), duration: 2, progress: 100, approved: true },
            { taskID: 10, taskName: 'Design Documentation', startDate: new Date('02/13/2017'), endDate: new Date('02/14/2017'), duration: 2, progress: 100, approved: true },
            { taskID: 11, taskName: 'Design complete', startDate: new Date('02/14/2017'), endDate: new Date('02/14/2017'), duration: 0, progress: 0, priority: 'Normal', approved: true }
        ]
    },
    {
        taskID: 12,
        taskName: 'Implementation Phase',
        startDate: new Date('02/17/2017'),
        endDate: new Date('02/27/2017'),
        priority: 'Normal',
        approved: false,
        duration: 11,
        subtasks: [
            {
                taskID: 13,
                taskName: 'Phase 1',
                startDate: new Date('02/17/2017'),
                endDate: new Date('02/27/2017'),
                priority: 'High',
                approved: false,
                duration: 11,
                subtasks: [{
                    taskID: 14,
                    taskName: 'Implementation Module 1',
                    startDate: new Date('02/17/2017'),
                    endDate: new Date('02/27/2017'),
                    priority: 'Normal',
                    duration: 11,
                    approved: false,
                    subtasks: [
                        { taskID: 15, taskName: 'Development Task 1', startDate: new Date('02/17/2017'), endDate: new Date('02/19/2017'), duration: 3, progress: '50', priority: 'High', approved: false },
                        { taskID: 16, taskName: 'Development Task 2', startDate: new Date('02/17/2017'), endDate: new Date('02/19/2017'), duration: 3, progress: '50', priority: 'Low', approved: true },
                        { taskID: 17, taskName: 'Testing', startDate: new Date('02/20/2017'), endDate: new Date('02/21/2017'), duration: 2, progress: '0', priority: 'Normal', approved: true },
                        { taskID: 18, taskName: 'Bug fix', startDate: new Date('02/24/2017'), endDate: new Date('02/25/2017'), duration: 2, progress: '0', priority: 'Critical', approved: false },
                        { taskID: 19, taskName: 'Customer review meeting', startDate: new Date('02/26/2017'), endDate: new Date('02/27/2017'), duration: 2, progress: '0', priority: 'High', approved: false },
                        { taskID: 20, taskName: 'Phase 1 complete', startDate: new Date('02/27/2017'), endDate: new Date('02/27/2017'), duration: 0, priority: 'Low', approved: true }

                    ]
                }]
            },
            {
                taskID: 21,
                taskName: 'Phase 2',
                startDate: new Date('02/17/2017'),
                endDate: new Date('02/28/2017'),
                priority: 'High',
                approved: false,
                duration: 12,
                subtasks: [{
                    taskID: 22,
                    taskName: 'Implementation Module 2',
                    startDate: new Date('02/17/2017'),
                    endDate: new Date('02/28/2017'),
                    priority: 'Critical',
                    approved: false,
                    duration: 12,
                    subtasks: [
                        { taskID: 23, taskName: 'Development Task 1', startDate: new Date('02/17/2017'), endDate: new Date('02/20/2017'), duration: 4, progress: '50', priority: 'Normal', approved: true },
                        { taskID: 24, taskName: 'Development Task 2', startDate: new Date('02/17/2017'), endDate: new Date('02/20/2017'), duration: 4, progress: '50', priority: 'Critical', approved: true },
                        { taskID: 25, taskName: 'Testing', startDate: new Date('02/21/2017'), endDate: new Date('02/24/2017'), duration: 2, progress: '0', priority: 'High', approved: false },
                        { taskID: 26, taskName: 'Bug fix', startDate: new Date('02/25/2017'), endDate: new Date('02/26/2017'), duration: 2, progress: '0', priority: 'Low', approved: false },
                        { taskID: 27, taskName: 'Customer review meeting', startDate: new Date('02/27/2017'), endDate: new Date('02/28/2017'), duration: 2, progress: '0', priority: 'Critical', approved: true },
                        { taskID: 28, taskName: 'Phase 2 complete', startDate: new Date('02/28/2017'), endDate: new Date('02/28/2017'), duration: 0, priority: 'Normal', approved: false }

                    ]
                }]
            },

            {
                taskID: 29,
                taskName: 'Phase 3',
                startDate: new Date('02/17/2017'),
                endDate: new Date('02/27/2017'),
                priority: 'Normal',
                approved: false,
                duration: 11,
                subtasks: [{
                    taskID: 30,
                    taskName: 'Implementation Module 3',
                    startDate: new Date('02/17/2017'),
                    endDate: new Date('02/27/2017'),
                    priority: 'High',
                    approved: false,
                    duration: 11,
                    subtasks: [
                        { taskID: 31, taskName: 'Development Task 1', startDate: new Date('02/17/2017'), endDate: new Date('02/19/2017'), duration: 3, progress: '50', priority: 'Low', approved: true },
                        { taskID: 32, taskName: 'Development Task 2', startDate: new Date('02/17/2017'), endDate: new Date('02/19/2017'), duration: 3, progress: '50', priority: 'Normal', approved: false },
                        { taskID: 33, taskName: 'Testing', startDate: new Date('02/20/2017'), endDate: new Date('02/21/2017'), duration: 2, progress: '0', priority: 'Critical', approved: true },
                        { taskID: 34, taskName: 'Bug fix', startDate: new Date('02/24/2017'), endDate: new Date('02/25/2017'), duration: 2, progress: '0', priority: 'High', approved: false },
                        { taskID: 35, taskName: 'Customer review meeting', startDate: new Date('02/26/2017'), endDate: new Date('02/27/2017'), duration: 2, progress: '0', priority: 'Normal', approved: true },
                        { taskID: 36, taskName: 'Phase 3 complete', startDate: new Date('02/27/2017'), endDate: new Date('02/27/2017'), duration: 0, priority: 'Critical', approved: false },
                    ]
                }]
            }
        ]
    }
];

零件

import { Component, OnInit,ViewChild } from '@angular/core';
import { sampleData } from '../datasource';

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

  constructor() { }

  @ViewChild('treegrid')
  public data: Object[];
  public foo: boolean;

  dropdown(e){
    console.log(e);
  }

  subtask(e){
    console.log(e);
    this.foo == false ? this.foo = true : this.foo = false;

  }

  ngOnInit(): void {
    this.data = sampleData;
}
}

Answer 1

您可以在模板中使用安全导航操作符?来解决它。这是stackbliz的工作演示

<H1>Table</H1>

<table *ngFor="let datum of data;" class="table table-bordered table-hover">
  <tr>
    <td class=""> </td>
    <td class="col-sm-2 col-md-2">{{datum?.taskID}}</td>
    <td class="col-sm-2 col-md-2">{{datum?.taskName}}</td>
    <td class="col-sm-2 col-md-2  btn btn.primary" (click)="dropdown(datum)">...</td>
  </tr>
  <div *ngIf="datum.subtasks">
  <table  *ngFor="let subtask of datum.subtasks">
      <tr>
          <td class="">> </td>
          <td class="col-sm-2 col-md-2">{{subtask?.taskID}}</td>
          <td class="col-sm-2 col-md-2">{{substask?.taskName}}</td>
          <td class="col-sm-2 col-md-2 btn btn.primary" (click)="dropdown(subtask)">...</td>
        </tr>
  </table>
  </div>