从Firebase数据库读取和显示数据 [英] reading and displaying data from a Firebase database

问题描述

我正在尝试从Firebase数据库检索数据，并将数据存储在我在课堂上定义的课程数组中.

I am trying to retreive data from a firebase database and store the data in a courses array i've defined in my class.

到目前为止，我已经知道了:

So far I've got :

import { AngularFireDatabase, AngularFireList } from 'angularfire2/database';
import { Router } from '@angular/router';
import { Component, OnInit } from '@angular/core';
import { AngularFireAuth } from 'angularfire2/auth';

@Component({
  selector: 'app-home-page',
  templateUrl: './home-page.component.html',
  styleUrls: ['./home-page.component.css']
})
export class HomePageComponent implements OnInit {


  courses:any[];


  constructor(public afAuth: AngularFireAuth,private router:Router,private db:AngularFireDatabase) { }

  ngOnInit() {

    if(this.afAuth.auth.currentUser){


        var ref = this.db.database.ref('/courses');

        ref.on("value", this.gotData, function (error) {
          console.log("Error: " + error.code);
        });


    }else{      
      this.router.navigate(['/login']);
    }

  }

  gotData(data){
    var x = data.val();
    console.log(x);
    this.courses = x; // >>>>>>>>>>>>>>>>>  ISSUE HERE
  }


}

但是我收到此错误消息:

However I am getting this error saying :

FIREBASE警告:用户回调引发了异常.TypeError:无法将属性课程"设置为空

FIREBASE WARNING: Exception was thrown by user callback. TypeError: Cannot set property 'courses' of null

和

错误TypeError:无法将属性"courses"设置为空

ERROR TypeError: Cannot set property 'courses' of null

我能够成功地控制台记录数据..但是我想存储这些数据.我该怎么办?

I am able to successfully console log the data.. but I want to store this data.. how can I do this?

推荐答案

错误消息告诉您 this 为空.为了确保保留它，将 gotData 定义为箭头函数:

The error message tells you that this is null. To ensure that it is preserved, define gotData as an arrow function:

gotData = (data) => {
   this.courses = data.val();
}

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