How to Add Local Notifications in Flutter?

class LocalNotificationService {
   // Instance of Flutternotification plugin
   static final FlutterLocalNotificationsPlugin _notificationsPlugin =
      FlutterLocalNotificationsPlugin(); 
}

static void initialize() {
    // Initialization  setting for android
    const InitializationSettings initializationSettingsAndroid =
        InitializationSettings(
            android: AndroidInitializationSettings("@drawable/ic_launcher"));
    _notificationsPlugin.initialize(
      initializationSettingsAndroid,
      // to handle event when we receive notification 
      onDidReceiveNotificationResponse: (details) {
        if (details.input != null) {}
      },
    );
  }

Future main() async {
  runApp(const MyApp());
}

class MyApp extends StatefulWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  State<MyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  @override
  void initState() {
    super.initState();
    // Initialise  localnotification
    LocalNotificationService.initialize();
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.green,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

firebase_messaging: 

Future main() async {
  FirebaseMessaging.onBackgroundMessage(backgroundHandler);
  // To handle background message
  runApp(const MyApp());
}

// background handler
Future backgroundHandler(RemoteMessage msg) async {}

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

    LocalNotificationService.initialize();
    
    // To initialise the sg
    FirebaseMessaging.instance.getInitialMessage().then((message) {
     
    });
    
    // To initialise when app is not terminated
    FirebaseMessaging.onMessage.listen((message) {
      if (message.notification != null) {
        LocalNotificationService.display(message);
      }
    });
    
    // To handle when app is open in 
    // user divide and heshe is using it
    FirebaseMessaging.onMessageOpenedApp.listen((message) {
     print("on message opened app");
    });
  }

static Future<void> display(RemoteMessage message) async {
    // To display the notification in device
    try {
      print(message.notification!.android!.sound);
      final id = DateTime.now().millisecondsSinceEpoch ~/ 1000;
      NotificationDetails notificationDetails = NotificationDetails(
        android: AndroidNotificationDetails(
            message.notification!.android!.sound ?? "Channel Id",
            message.notification!.android!.sound ?? "Main Channel",
            groupKey: "gfg",
            color: Colors.green, 
            importance: Importance.max,
            sound: RawResourceAndroidNotificationSound(
                message.notification!.android!.sound ?? "gfg"),
          
            // different sound for 
            // different notification
            playSound: true,
            priority: Priority.high),
      );
      await _notificationsPlugin.show(id, message.notification?.title,
          message.notification?.body, notificationDetails,
          payload: message.data['route']);
    } catch (e) {
      debugPrint(e.toString());
    }

// in some device or platform specially in web
// it may happen gettoken is not supported then 
// you can put these condition to so that
// you can not get any error in production
var notifyToken = FirebaseMessaging.instance.isSupported()
                                            ? await FirebaseMessaging.instance
                                                .getToken()
                                            : "notifyToken";

void messageListener(BuildContext context) {
    // Either you can pass buildcontext or you
      // can take a context from navigator key
    FirebaseMessaging.onMessage.listen((RemoteMessage message) {
      print('Got a message in the foreground!');
      print('Message data: ${message.data}');

      if (message.notification != null) {
        print(
            'Message also contained a notification:  so it will pop up ${message.notification.body}');
        showDialog(
            context: context,
            // context: navigatorKey!.currentContext!,
            builder: ((BuildContext context) {
              return DynamicDialog(
                  title: message.notification.title,
                  body: message.notification.body);
            }));
      }
    });
  }

import 'package:flutter/material.dart';

class DynamicDialog extends StatefulWidget {
  final title;
  final body;
  const DynamicDialog({this.title, this.body});
  @override
  _DynamicDialogState createState() => _DynamicDialogState();
}

class _DynamicDialogState extends State<DynamicDialog> {
  @override
  Widget build(BuildContext context) {
    // You can change the UI as per
    // your requirement or choice
    return AlertDialog(
      title: Text(widget.title),
      actions: <Widget>[
        OutlinedButton.icon(
            label: const Text('Close'),
            onPressed: () {
              Navigator.pop(context);
            },
            icon: const Icon(Icons.close))
      ],
      content: Text(widget.body),
    );
  }
}

@override
void initState() {
    super.initState();
    LocalNotificationService.initialize();
    LocalNotificationService.messageListener(context);
    FirebaseMessaging.onBackgroundMessage(backgroundHandler);
    FirebaseMessaging.instance.getInitialMessage().then((message) {
      print("Initial Message ${message.toString()}");
    });
    FirebaseMessaging.onMessageOpenedApp.listen((event) {
      print("Message on App opened ${event.toString()}");
    });
    FirebaseMessaging.onMessage.listen((event) {
      print("Message when it is termination mode ${event.toString()}");
      if (event.notification != null) {
        LocalNotificationService.display(event);
      }
    });
  }