multithreading - 代码在从Firebase获取数据之前////Angular 2

Question

我尝试从firebase及其成功中获取数据，但需要花费几秒钟的时间，
代码继续，因此变量的值为null。
为什么会这样呢？它是线程的吗？我该怎么办？

gameslist.component.ts

        import {Component} from 'angular2/core';
        import {Game} from './Game'
        import {NgStyle} from "angular2/common";
        import {DataService} from "./data.service";

        declare var firebase: any;

        @Component({
            selector:'gameslist',
            templateUrl: 'app/ts/gameslist.component.html',
            styleUrls: ['app/ts/gameslist.component.css'],
            inputs: ['games'],
            directives: [NgStyle],
            providers:[DataService]

        })

        export class gamesListComponent{
            public games;
            public currentGame=[];
            public votes1: number;
        constructor(private dataService:DataService){ this.votes1=0;this.currentGame=[];}

            fbPostVote(id_game:number,ChooseVote:number){
                this.votes1=this.dataService.getGameById(id_game);   //Here return null     
                this.votes1++;
                var updates = {};
                updates['/games/'+id_game+'/rec_1_votes'] = this.votes1;
                updates['/games/'+id_game+'/rec_1_color'] = 'pink';
                this.games[id_game].rec_1_color = 'pink';    
                return firebase.database().ref().update(updates);
}

data.service.ts

       import {Injectable} from 'angular2/core';
        import {Http, Response} from 'angular2/http';
         import 'rxjs/Rx'; 

         @Injectable()   
          export class DataService{

        constructor(private http:Http){        }         

        getGameById(id_game:number){
              firebase.database().ref('/games/'+id_game+'/rec_1_votes').on('value',function(snap) { 
               return snap.val();
                 });
             }
     }

谢谢。

Answer 1

getGameById()不返回任何内容。更改为

    getGameById(id_game:number){
          return firebase.database().ref('/games/'+id_game+'/rec_1_votes').on('value',function(snap) { 
           return snap.val();
             });
         }