问在角飞镖中填充Firebase数据库列表

EN

import 'package:angular/angular.dart';
import 'package:firebase/firebase.dart' as fb;
import 'package:yns_admin/category_component/category.dart';

@Injectable()
class FirebaseService {

  fb.Database fbDatabase;
  fb.DatabaseReference databaseReference;

  List<Category> categories;

  FirebaseService() {
    fb.initializeApp(
      apiKey: "AIzaSyBOShlCgUeqTL99n32ssasasasasa",
      authDomain: "yns-app.firebaseapp.com",
      databaseURL: "https://yns-app.firebaseio.com",
      storageBucket: "yns-app.appspot.com",
    );

    fbDatabase = fb.database();
    databaseReference = fbDatabase.ref("categories");
  }

  void showCategories() {
    categories = [];
    databaseReference.onChildAdded.listen(newCategory);
  }

  void newCategory(fb.QueryEvent event) {

    Category category = new Category.fromMap(event.snapshot.val());
    categories.add(category);
  }
}

  class Category {

  final String categoryTitle;

  Category(this.categoryTitle);

  Category.fromMap(Map map, this.categoryTitle) {}

  Map toMap() =>{
    "categoryTitle":categoryTitle
  };
}

import 'package:angular/angular.dart';
import 'package:yns_admin/app_component/app_component.dart';

void main() {
  bootstrap(AppComponent);
}