Flutter equivalent to Swift's NotificationCenter? - dart

Question

I'm using FirebaseMessaging to send push notifications to my Flutter app. Those notifications contain chat details.
If the app is currently active and the user is at the chat page, the page should be updated to show the new message (this I can handle).
If the app is on any other page, a local notification/toast should be shown.
My problem, how do I forward the notification to the chat page?
I have FirebaseMessaging listening on the root page. And I can use ModalRoute.of(context).isCurrent to determine if the root page is the current page when the notification comes in. How can I broadcast the notification to the chat page when it is the active page?
In Swift, I'd use NotificationCenter to send data from the app delegate and the chat page would listen for it. I'm hoping something similar is available for Flutter.

Answer 1

Try this dart-event-bus.
An Event Bus using Dart Streams for decoupling applications

Answer 2

I've found a solution and I'm hoping it can help someone else in a similar situation.
I found the package Dart Message Bus
It does everything I need and make handling Streams much easier.
I did have to add one additional method (see the end).
Since the instructions were a bit cryptic, here's how I got it working.
//main.dart
import 'package:dart_message_bus/dart_message_bus.dart';
//global variable
final globalBus = new MessageBus();
class _MyHomePageState extends State<MyHomePage> {
// set up firebase messaging here
#override
void initState() {
super.initState();
_setupPushNotifs;
}
_setupPushNotifs() {
_firebaseMessaging.configure(
onMessage: (Map<String, dynamic> message) {
_processChatPush(message);
},
);
}
_processChatPush(Map<String, dynamic> message) async {
String messageID = message['messageID'];
globalBus.publish(new Message('newChat', data: "$messageID"));
}
}
//chat.dart
import 'package:dart_message_bus/dart_message_bus.dart';
import 'main.dart';
class _ChatPageState extends State<ChatPage> {
StreamSubscription streamListener;
#override
void initState() {
super.initState();
_listen();
}
#override
void dispose() {
streamListener.cancel();
streamListener = null;
}
_listen() async {
streamListener = globals.globalBus.subscribe('newChat', (Message m) async {
Map<String, dynamic> message = m.data;
String messageID = message['messedID'];
}
}
The dispose method is very important or the listener will keep listening and cause problems.
If you need verification that a subscriber is actually listening, modify the calling and listen methods:
// main.dart
_processChatPush(Map<String, dynamic> message) async {
String messageID = message['messageID'];
var callbackMessage = await globalBus.publish(
new Message('newChat', data: "$messageID"),
waitForKey: 'ackChat',
timeout: const Duration(seconds: 2)
);
if(callbackMessage.isEmpty) {
// means the another service's message was not received
// and timeout occured.
// process the push notification here
} else {
// the callback from another service received
// and callbackMessage.data contains callback-data.
// the push notification has been handled by chat.dart
}
}
// chat.dart
_listen() async {
streamListener = globals.globalBus.subscribe('newChat', (Message m) async {
Map<String, dynamic> message = m.data;
String messageID = message['messageID'];
var data = "ack";
var ack = new Message('ackChat', data: data);
globalBus.publish(ack);
}
}
I had to add one additional method in order to close the publishing stream when it's no longer needed.
Add to the end of Class MessageBus in message_bus.dart in the package source:
close() {
_streamController.close();
_streamController = null;
}
and then you can dispose the stream:
void dispose() {
globalBus.close();
super.dispose();
}
I ended up putting the globalBus variable in a library file. Then import that library in main.dart and chat.dart and remove the import main.dart from chat.dart.