Angular 2 - 未捕获（承诺）：TypeError：无法读取未定义的属性“标题”答案

【问题标题】：Angular 2 - Uncaught (in promise): TypeError: Cannot read property 'title' of undefinedAngular 2 - 未捕获（承诺）：TypeError：无法读取未定义的属性“标题”
【发布时间】：2023-03-14 00:32:01
【问题描述】：

当我尝试添加一些具有双重绑定的文本输入字段时，我在我的应用程序中看到此错误：

   ERROR Error: Uncaught (in promise): TypeError: Cannot read property 'title' of undefined
TypeError: Cannot read property 'title' of undefined
    at Object.eval [as updateRenderer] (ng:///AppModule/TapesComponent.ngfactory.js:660:29)
    at Object.debugUpdateRenderer [as updateRenderer] (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12658:21)
    at checkAndUpdateView (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12037:14)
    at callViewAction (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12347:17)
    at execComponentViewsAction (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12293:13)
    at checkAndUpdateView (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12038:5)
    at callWithDebugContext (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:13020:42)
    at Object.debugCheckAndUpdateView [as checkAndUpdateView] (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12560:12)
    at ViewRef_.detectChanges (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:10129:63)
    at RouterOutlet.activateWith (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:5378:42)
    at ActivateRoutes.placeComponentIntoOutlet (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4558:16)
    at ActivateRoutes.activateRoutes (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4539:26)
    at eval (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4475:58)
    at Array.forEach (native)
    at ActivateRoutes.activateChildRoutes (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4475:29)
    at Object.eval [as updateRenderer] (ng:///AppModule/TapesComponent.ngfactory.js:660:29)
    at Object.debugUpdateRenderer [as updateRenderer] (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12658:21)
    at checkAndUpdateView (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12037:14)
    at callViewAction (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12347:17)
    at execComponentViewsAction (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12293:13)
    at checkAndUpdateView (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12038:5)
    at callWithDebugContext (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:13020:42)
    at Object.debugCheckAndUpdateView [as checkAndUpdateView] (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:12560:12)
    at ViewRef_.detectChanges (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:10129:63)
    at RouterOutlet.activateWith (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:5378:42)
    at ActivateRoutes.placeComponentIntoOutlet (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4558:16)
    at ActivateRoutes.activateRoutes (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4539:26)
    at eval (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4475:58)
    at Array.forEach (native)
    at ActivateRoutes.activateChildRoutes (http://localhost:3000/node_modules/@angular/router/bundles/router.umd.js:4475:29)
    at resolvePromise (http://localhost:3000/node_modules/zone.js/dist/zone.js:712:31) [angular]
    at resolvePromise (http://localhost:3000/node_modules/zone.js/dist/zone.js:683:17) [angular]
    at http://localhost:3000/node_modules/zone.js/dist/zone.js:760:17 [angular]
    at Object.onInvokeTask (http://localhost:3000/node_modules/@angular/core/bundles/core.umd.js:4123:37) [angular]
    at ZoneDelegate.invokeTask (http://localhost:3000/node_modules/zone.js/dist/zone.js:397:36) [angular]
    at Zone.runTask (http://localhost:3000/node_modules/zone.js/dist/zone.js:165:47) [<root> => angular]
    at drainMicroTaskQueue (http://localhost:3000/node_modules/zone.js/dist/zone.js:593:35) [<root>]
    at HTMLAnchorElement.ZoneTask.invoke (http://localhost:3000/node_modules/zone.js/dist/zone.js:464:25) [<root>]

我有这个磁带类：

    export class Tape {
  constructor (
  public id: number,
  public title: string,
  public date?: string,
  public rating?: number,
  public description?: string,
  public photo?: string){}
}

和组件

import { Component, OnInit } from '@angular/core';
import { Tape } from './tape'
import { TapeService } from './tape.service';
import { Router } from '@angular/router';
// import { TitlePipe } from './titleFilter';

@Component({
  selector: 'my-tapes',
  templateUrl: './tapes.component.html',
  styleUrls: [`./tapes.component.css`],
  providers: [TapeService],

})
export class TapesComponent implements OnInit {
  pageName = 'VHS Movies listing';
  tapes: Tape[];
  selectedTape: Tape;
  model = new Tape(0,'s','s',0,'s','sS');

组件 HTML 看起来像

<div class="form-group">
              <label for="title">Title{{model.title}}</label>
              <input type="text" class="form-control" id="title" required [(ngModel)]="model.title" name="title" #title="ngModel">              Written text: {{tape.title}}
              <div [hidden]="title.valid || title.pristine" class="alert alert-danger">
                Title is mandatory
              </div>
            </div>

我刚开始学习 Angular 2，但对我来说它应该从模块中获得标题。他看不懂标题？

【问题讨论】：

试试{{model?.title}}
使用安全导航 (?)，例如 model?title
@echonax，我还在等你为这个undefined 问题做问答：P 你在异步问题上做得很好；）
@AJT_82 谢谢 :-) 你也可以这样做；P

标签： angular

【解决方案1】：

尝试使用 safe /elvis 运算符检查值是否存在然后显示，

 <input type="text" class="form-control" id="title" required [(ngModel)]="model?.title" name="title" #title="ngModel"> Written text: {{model?.title}}

【讨论】：

你知道? 对程序的性能和速度有影响吗？

【解决方案2】：

我没有使用 Elvis 运算符，而是首先将对象定义为空对象，然后通过服务调用分配所需的值。

model = <model>{}
//here goes service call

【讨论】：

【解决方案3】：

你是对的：

Written text: {{tape.title}}

应该是

Written text: {{module.title}}

愚蠢的错误！谢谢！

【讨论】：

【解决方案4】：

我在使用时也出现了同样的问题，所以我给出了不同的名称，例如 [(ngModel)]="pranav" 而不是 model.pranav。然后问题就解决了。

在 ngModel 和 #name 中使用不同的名称，否则会产生歧义

【讨论】：