Example for http://stackoverflow.com/questions/41659368/angularfire2-access-data-after-retrieve-it/41663265#41663265

my-page.ts

import { Component } from '@angular/core';
import { NavController, NavParams } from 'ionic-angular';
import { MyService } from '../../providers/my-service';
import { AnotherPage } from '../another-page/another';
import 'rxjs/add/operator/filter';

/*
  Generated class for the MyPage page.

  See http://ionicframework.com/docs/v2/components/#navigation for more info on
  Ionic pages and navigation.
*/
@Component({
  selector: 'page-my-page',
  templateUrl: 'my-page.html'
})
export class MyPage {

  constructor(
    public navCtrl: NavController, 
    public navParams: NavParams, 
    private _myService : MyService) {}

  ionViewDidLoad() {
    console.log('ionViewDidLoad MyPagePage');

    // I JUST WANT TO CHANGE TO ANOTHER PAGE WHEN reg_boolean IT's TRUE
    this._myService.getRegBoolean().filter(regBoolean => regBoolean === true)
      .subscribe( () =>  this.navCtrl.push(AnotherPage));

  }

}

my-service.ts

import { Injectable } from '@angular/core';
import 'rxjs/add/operator/map';
import {Observable} from "rxjs";
import {AngularFire} from "angularfire2";

/*
  Generated class for the MyService provider.

  See https://angular.io/docs/ts/latest/guide/dependency-injection.html
  for more info on providers and Angular 2 DI.
*/
@Injectable()
export class MyService {

  constructor(private af : AngularFire) {
    console.log('Hello MyService Provider');
  }

  getRegBoolean() : Observable<boolean> {
    return this.af.database.list('/users/1qfcMAQnglX9jsW5GdLpPko1HqE2', { preserveSnapshot: true})
    .map(snapshots=>{

        snapshots.forEach(snapshot => {
          if(snapshot.key=="reg_boolean"){
            return snapshot.val();
          }
        });

        return false;

    });

  }

}