无法读取angular2中未定义的属性

Question

我正在使用Angular 2并正在进行API调用以获取一些JSON.通话有效,我收到回复.

export class DetailsPage {

  public userID;
  v: any = {};           

  constructor(public navCtrl: NavController, public navParams: NavParams, public http: Http) {

    this.userID = navParams.get('userID');

    var headers = new Headers();
    headers.append('Content-Type', 'application/x-www-form-urlencoded');  

    let urlSearchParams = new URLSearchParams();
    let body = urlSearchParams.toString();

    this.http.get('http://api.domain.com/visitor/'+this.userID, {headers:headers}).map(res => res.json()).subscribe(data => {
        this.v = data.res;
    }); 

  }

}

在我的模板中,我有:

<pre>{{v | json}}</pre>

这告诉我我的JSON ......

{
  "user": {
    "id": "794149",
    "tag_name": "",
    "tag_id": "0",
    "tag_style": {
      "color": null,
      "font": null,
      "style": "label-default"
    }
  },

但是如何显示用户的ID？

我试过了 ..

{{ v.user.id }}

但这给了我一个错误:

Error in ./DetailsPage class DetailsPage -  caused by: Cannot read property 'id' of undefined

Answer 1

绑定到对象上的属性可以为null使用安全导航操作符"？" .

   {{v?.user?.id}}