angular - 从 Firebase 数据库读取和显示数据

Question

我正在尝试从 Firebase 数据库检索数据并将数据存储在我在类(class)中定义的类(class)数组中。

到目前为止我已经得到:

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:

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

和

ERROR TypeError: Cannot set property 'courses' of null

我能够成功地控制台记录数据..但我想存储这些数据..我该怎么做？

Answer 1

错误消息告诉您this为空。为了确保它被保留，请将 gotData 定义为箭头函数:

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