Push notifications with Firebase Cloud Messaging and Flutter

main_page.dart

import 'package:flutter/material.dart';
import '../utils/util.dart';
import '../controllers/push_notifications.dart';

class MainPage extends StatefulWidget {
  @override
  _MainPageState createState() => _MainPageState();
}

class _MainPageState extends State<MainPage> {
  @override
  void initState() {
    PushNotifications().notification.listen((notification) => _handleNotification(notification));
    super.initState();
  }

  _handleNotification(notification) {
    print('===== HANDLE NOTIFICATION =====');
    if (notification == null || context == null) return;
    var title = notification['notification']['title'] ?? "Notification";
    var body = notification['notification']['body'] ?? "";

    Util.showMessageDialog(context, title, body);
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      
    );
  }
}

push_notifications.dart

import 'dart:async';
import 'dart:convert';
import 'dart:io';

import 'package:firebase_messaging/firebase_messaging.dart';
import '../config/config.dart';
import '../utils/user_preferences.dart';

class PushNotifications {
  static final PushNotifications _instance = PushNotifications._internal();
  factory PushNotifications() => _instance;
  PushNotifications._internal();

  final FirebaseMessaging _firebaseMessaging = FirebaseMessaging();

  bool _isConfigured = false;

  var _tokenStreamController = StreamController<String>.broadcast();
  Stream<String> get token => _tokenStreamController.stream;

  var _notificationStreamController = StreamController<Map<String, dynamic>>.broadcast();
  Stream<Map<String, dynamic>> get notification => _notificationStreamController.stream;

  init() {
    // Request push permissions
    _firebaseMessaging.requestNotificationPermissions();

    // Get device token
    _firebaseMessaging.getToken().then((token) {
      print('===== FCM Token =====');
      print(token);
      _saveDeviceToken(token);
    });

    // Configure messaging receiving
    if (!_isConfigured) {
      _firebaseMessaging.configure(
          onMessage: (info) async {
            print('======= On Message =======');
            print(info);
            _setStreamData(info);
          },
          onLaunch: (info) async {
            print('======= On Launch =======');
            print(info);
            _setStreamData(info);
          },
          onResume: (info) async {
            print('======= On Resume =======');
            print(info);
            _setStreamData(info);
          },
          onBackgroundMessage: Platform.isAndroid ? backgroundMessageHandler : null
      );
      _isConfigured = true;
    }
  }

  static Future<dynamic> backgroundMessageHandler(Map<String, dynamic> notInfo) async {    
    return Future.value();
  }

  _setStreamData(Map<String, dynamic> notInfo) {
    Map<String, dynamic> notification = Map<String, dynamic>();
    if (notInfo != null) {
      if (notInfo.containsKey('aps')) {
        var not = {'title': notInfo['aps']['alert']['title'], 'body': notInfo['aps']['alert']['body']};
        notification['notification'] = not;
        notInfo.remove('aps');
        notification['data'] = notInfo;
      } else if (notInfo.containsKey('notification') && notInfo.containsKey('data')) {
        notification = notInfo;
      } else if (notInfo.containsKey('notification') && !notInfo.containsKey('data')) {
        notification['notification'] = notInfo['notification'];
        notInfo.remove('notification');
        notification['data'] = notInfo;
      }

      print('===== STREAM NOTIFICATION =====');
      print(notification);
      _notificationStreamController.sink.add(notification);
    }
  }
  
  _saveDeviceToken(token) async {
    await UserPreferences.setString(config.deviceTokenPrefId, token);
    _tokenStreamController.sink.add(token);
  }

  Future<String> getDeviceToken() async {
    return await UserPreferences.getString(config.deviceTokenPrefId);
  }

  dispose() {
    _notificationStreamController?.close();
    _tokenStreamController?.close();
  }
}

root_page.dart

import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import '../controllers/login_controller.dart';
import '../controllers/push_notifications.dart';
import './login_page.dart';
import './customers_page.dart';
import '../controllers/user_controller.dart';

class RootPage extends StatefulWidget {
  @override
  _RootPageState createState() => _RootPageState();
}

class _RootPageState extends State<RootPage> {
  var _userLoggedIn;
  UserController _userController;
  String _deviceToken;

  @override
  void initState() {
    super.initState();

    PushNotifications().token.listen((token) => _handleToken(token));

    _deviceToken = null;
    _userController = UserController();
  }

  _handleToken(token) async {
    print('===== HANDLE TOKEN =====');
    print(token);
    if (_deviceToken == null || _deviceToken == "") {
      var loginController = LoginController();
      var result = await loginController.setDeviceToken(token);
      print('===== TOKEN SENT TO SERVER =====');
      print('Result: $result');
    }
  }

  void checkDeviceToken() async {
    var deviceToken = await PushNotifications().getDeviceToken();
    setState(() {
      _deviceToken = deviceToken;
    });
    PushNotifications().init();
  }

  @override
  void dispose() {
    PushNotifications().dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    if (!_userLoggedIn) {
      return LoginPage(onLoggedIn: _loggedIn);
    }
    return CustomersPage(onLoggedOut: _loggedOut);
  }
}