main.dart

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_core/firebase_core.dart';
import 'package:firebase_messaging/firebase_messaging.dart';
import 'package:flutter/material.dart';
import 'package:flutter_local_notifications/flutter_local_notifications.dart';

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  await Firebase.initializeApp();
  print('Handling a background message ${message.messageId}');
  print(message.data);
  flutterLocalNotificationsPlugin.show(
      message.data.hashCode,
      message.data['title'],
      message.data['body'],
      NotificationDetails(
        android: AndroidNotificationDetails(
          channel.id,
          channel.name,
          channel.description,
        ),
      ));
}

const AndroidNotificationChannel channel = AndroidNotificationChannel(
  'high_importance_channel', // id
  'High Importance Notifications', // title
  'This channel is used for important notifications.', // description
  importance: Importance.high,
);

final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
    FlutterLocalNotificationsPlugin();

void main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await Firebase.initializeApp();

  FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
  await flutterLocalNotificationsPlugin
      .resolvePlatformSpecificImplementation<
          AndroidFlutterLocalNotificationsPlugin>()
      ?.createNotificationChannel(channel);

  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  String token;
  List subscribed = [];
  List topics = [
    'Samsung',
    'Apple',
    'Huawei',
    'Nokia',
    'Sony',
    'HTC',
    'Lenovo'
  ];
  @override
  void initState() {
    super.initState();
    var initialzationSettingsAndroid =
        AndroidInitializationSettings('@mipmap/ic_launcher');
    var initializationSettings =
        InitializationSettings(android: initialzationSettingsAndroid);

    flutterLocalNotificationsPlugin.initialize(initializationSettings);
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      RemoteNotification notification = message.notification;
      AndroidNotification android = message.notification?.android;
      if (notification != null && android != null) {
        flutterLocalNotificationsPlugin.show(
            notification.hashCode,
            notification.title,
            notification.body,
            NotificationDetails(
              android: AndroidNotificationDetails(
                channel.id,
                channel.name,
                channel.description,
                icon: android?.smallIcon,
              ),
            ));
      }
    });
    getToken();
    getTopics();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
          appBar: AppBar(
            title: Text('appbar'),
          ),
          body: ListView.builder(
            itemCount: topics.length,
            itemBuilder: (context, index) => ListTile(
              title: Text(topics[index]),
              trailing: subscribed.contains(topics[index])
                  ? ElevatedButton(
                      onPressed: () async {
                        await FirebaseMessaging.instance
                            .unsubscribeFromTopic(topics[index]);
                        await FirebaseFirestore.instance
                            .collection('topics')
                            .doc(token)
                            .update({topics[index]: FieldValue.delete()});
                        setState(() {
                          subscribed.remove(topics[index]);
                        });
                      },
                      child: Text('unsubscribe'),
                    )
                  : ElevatedButton(
                      onPressed: () async {
                        await FirebaseMessaging.instance
                            .subscribeToTopic(topics[index]);

                        await FirebaseFirestore.instance
                            .collection('topics')
                            .doc(token)
                            .set({topics[index]: 'subscribe'},
                                SetOptions(merge: true));
                        setState(() {
                          subscribed.add(topics[index]);
                        });
                      },
                      child: Text('subscribe')),
            ),
          )),
    );
  }

  getToken() async {
    token = await FirebaseMessaging.instance.getToken();
    setState(() {
      token = token;
    });
    print(token);
  }

  getTopics() async {
    await FirebaseFirestore.instance
        .collection('topics')
        .get()
        .then((value) => value.docs.forEach((element) {
              if (token == element.id) {
                subscribed = element.data().keys.toList();
              }
            }));

    setState(() {
      subscribed = subscribed;
    });
  }
}