Angular 2：{{object}}起作用，{{object.child}}抛出错误

问题描述

已经和Angular v1合作已经有一段时间了，自从Angular v2进入测试阶段以来，一直在玩这个。

Been working with Angular v1 for some time now and since Angular v2 came in Beta, been playing around with that.

现在我有了这段代码，但不能让它上班，真的不知道为什么。不知何故，当我打印 {{profileUser | json}} 一切正常（profileUser是一个对象）。

Now I've got this piece of code, but can't get it to work, really don't know why. Somehow, when I print {{profileUser | json}} everything works fine (profileUser is an object).

但是当我想打印那个对象的子节点时（例如 {{profileUser.name}} 或 {{profileUser.name.firstName}} ），Angular会抛出以下错误：

But when I want to print a child of that object (for example {{profileUser.name}} or {{profileUser.name.firstName}}), Angular throws the following error:

EXEPTION：TypeError：undefined不是ProfileComponent @中{{{profileUser.name}}中的对象（评估'l_profileUser0.name'） 4:11 。

这对我来说真的很混乱，应该只是最简单的事情之一..刚开始使用TypeScript btw ..

It's really confusing to me, should be just one of the simplest things around.. Just started with TypeScript btw..

这是一些代码 - ProfileService.ts ：

Here is some code - ProfileService.ts:

import { Injectable } from 'angular2/core';
import { Headers } from 'angular2/http';
import { API_PREFIX } from '../constants/constants';
import { AuthHttp } from 'angular2-jwt/angular2-jwt';
import 'rxjs/add/operator/map';

@Injectable()
export class ProfileService {

  API_PREFIX = API_PREFIX;

  constructor(private _authHttp:AuthHttp) {
  }

  getProfileData(username:string):any {
    return new Promise((resolve, reject) => {
      this._authHttp.get(API_PREFIX + '/users/username/' + username)
        .map(res => res.json())
        .subscribe(
          data => {
            resolve(data.data);
          },
          err => {
            reject(err);
          }
        )
      ;
    });
  }
}

这是我的 ProfileComponent ：

import {Component, OnInit} from 'angular2/core';
import {RouteParams} from 'angular2/router';
import {ProfileService} from '../../services/profile.service';

@Component({
  selector: 'profile',
  templateUrl: './components/profile/profile.html',
  directives: [],
  providers: [ProfileService]
})

export class ProfileComponent implements OnInit {

  public username:string;
  public profileUser:any;

  constructor(private _profileService: ProfileService,
              private _params: RouteParams) {
    this.username = this._params.get('username');
  }

  ngOnInit() {
    this.getProfileData(this.username);
  }

  getProfileData(username:string):void {
    this._profileService.getProfileData(username)
      .then(data => {
        this.profileUser = data;
        console.log(data);
      })
    ;
  }
}

最后，个人资料。 html 模板：

<pre> <!-- works! -->
{{profileUser | json}}
</pre>

或..

<pre> <!-- throws the error -->
{{profileUser.name | json}}
</pre>

或..

<pre> <!-- throws the error -->
{{profileUser.name.firstName}}
</pre>

仅供参考，profileUser如下所示：

FYI, the profileUser looks like this:

{
  "id": "9830ecfa-34ef-4aa4-86d5-cabbb7f007b3",
  "name": {
    "firstName": "John",
    "lastName": "Doe",
    "fullName": "John Doe"
  }
}

如果有人可以帮助我，那会很棒，这真的让我回过头来熟悉Angular v2。谢谢！

Would be great if somebody could help me out, this is really holding me back to get familiar with Angular v2. Thanks!

推荐答案

实际上你的 profileUser 对象是从HTTP加载的请求，它可以在开头 null 。 json 管道只执行 JSON.stringify 。

In fact your profileUser object is loaded from an HTTP request and it can be null at the beginning. The json pipe simply does a JSON.stringify.

这是您的错误消息所说的： undefined不是对象（评估'l_profileUser0.name'）。

It's what your error message said: undefined is not an object (evaluating 'l_profileUser0.name').

您需要确保 profileUser 对象不为null才能获取其 name 属性等等。这可以使用 * ngIf 指令来完成：

You need to be sure that your profileUser object isn't null to be able to get its name attribute and so on. This can be done using an *ngIf directive:

<div *ngIf="profileUser">
  {{profileUser.name | json}}
</div>

当数据存在时，将显示HTML块。

When the data will be there, the HTML block will be displayed.

表示，Elvis运营商也可以为您提供帮助。而不是 {{profileUser.name | json}} ，您可以使用 {{profileUser？.name | json}} 。

As Eric stated the Elvis operator could also help you. Instead of having {{profileUser.name | json}}, you could use {{profileUser?.name | json}}.

希望它可以帮到你，
Thierry

Hope it helps you,Thierry

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