javascript - angular2中的 typescript ，如何通过这个访问类变量

Question

鉴于此代码，我如何访问对象“ session ”？由于“this”为空而失败:

/// <reference path="chrome/chrome-app.d.ts" />

import { Component, Input, OnInit } from '@angular/core';
import { AppService } from './app.service';

@Component({
    selector: 'tabs',
    templateUrl: './templates/app.html',
    providers: [ AppService ]
})

export class AppComponent implements OnInit {
    public sessions : Object;
    constructor( private appService : AppService ) {}

    getBookmarkLists() {
        console.log(this.sessions) // it gives undefined
        this.sessions['test'] = 'yea'; // it fails
        this.appService.getBookmarks().then(function(bookmarks : any) {
            console.log(this.sessions) // it fails
        });

    }

    ngOnInit() {
        this.getBookmarkLists();
    }
 }

我希望能够访问变量并填充它。

Answer 1

你没有在任何地方初始化这个Sessions对象，据我所知应该是:

export class AppComponent implements OnInit {
    public sessions: Session[] = []; // You forgot here to initialize it
    constructor( private appService : AppService ) {}

    getBookmarkLists() {
        console.log(this.sessions) // no it shouldn't give undefined
        this.sessions['test'] = 'yea'; // and this shouldn't fail
        this.appService.getBookmarks().then((bookmarks : any) => {
            // this should be an arrow function or function bound to use it
            // otherwise this will point to the function itself.
            console.log(this.sessions) // it shouldn't fail
        });

    }

    ngOnInit() {
        this.getBookmarkLists();
    }
}

sessions = []; 是关键部分。因此，这不仅仅是 this 的问题，它在方法中按应有的方式引用了类实例。

传递给 then 的回调函数应该是箭头函数而不是 classic 函数，以保持 this 对类实例的引用。