Angular 中的签入组件为空

Question

我有一个 Angular 8 应用程序。但是我收到这个错误：在一个组件上。它是一个组件中的一个组件。如果组件为空，则将显示错误，如果组件不为空，则不会显示错误:4200/dossier-dossier-module-ngfactory.js:186 ERROR TypeError: Cannot read property 'length' of null    at DossierCorrespondenceItemComponent.push../src/app/dossier/dossier-correspondence-item/dossier-correspondence-item.component.ts.DossierCorrespondenceItemComponent.ngOnInit (:4200/dossier-dossier-module-ngfactory.js:100)    at checkAndUpdateDirectiveInline (vendor.js:37850)    at checkAndUpdateNodeInline (vendor.js:46063)    at checkAndUpdateNode (vendor.js:46025)    at debugCheckAndUpdateNode (vendor.js:46659)    at debugCheckDirectivesFn (vendor.js:46619)    at Object.updateDirectives (:4200/dossier-dossier-module-ngfactory.js:189)    at Object.debugUpdateDirectives [as updateDirectives] (vendor.js:46611)    at checkAndUpdateView (vendor.js:46007)    at callViewAction (vendor.js:46248)在这个组件上：  <app-dossier-correspondence-item    [item]="single"    (goBack)="goBack($event)"    *ngIf="showingSingle">  </app-dossier-correspondence-item></app-vital10-page>这是 ts 代码：import { Component, OnInit } from '@angular/core';import { HealthAPIService } from '../../shared/health-api/health-api.service';import { DossierEntry } from '../../interfaces/dossier/dossier-entry.interface';@Component({  selector: 'app-dossier-correspondence',  templateUrl: './dossier-correspondence.component.html',})export class DossierCorrespondenceComponent implements OnInit {  allCorrespondence: Array<DossierEntry>;  correspondenceEntries: Array<DossierEntry>;  attachmentEntries: Array<DossierEntry>;  message = '';  emptyMessage = 'Geen correspondentie.';  errorMessage = 'Er ging iets mis met de connectie. Probeer over enkele minuten nogmaals.';  correspondenceLoaded = false;  showingSingle = false;  single: DossierEntry;那么如何解决这个问题呢？谢谢你。所以会很好地解决这个问题

Answer 1

当您在 gotoItem 中将 ShowingSingle 设置为 true 时，将启用该元素。但是在您启用它的那一刻，您的单身还没有设置。请在您的开关箱之后将 ShowingSingle 设置为 true。

gotoItem(index, type: string) {

    // NOT HERE

    switch (type) {

      case 'correspondence': {

        this.single = this.correspondenceEntries[index];

        break;

      }

      case 'attachments': {

        this.single = this.attachmentEntries[index];

        break;

      }

      default: {

        break;

      }

    }

    this.showingSingle = true; // BUT HERE

  }