listen to app lifecycle and send presence

Author: Wahid Nasri

lib/MqttImpl/MqttChatEventsSender.dart

@@ -3,10 +3,12 @@ import 'package:flutter_mqtt/abstraction/ChatEventsSender.dart';
 import 'package:flutter_mqtt/abstraction/ClientHandler.dart';
 import 'package:flutter_mqtt/abstraction/models/ChatMarkerMessage.dart';
 import 'package:flutter_mqtt/abstraction/models/InvitationMessage.dart';
+import 'package:flutter_mqtt/abstraction/models/PresenceMesssage.dart';
 import 'package:flutter_mqtt/abstraction/models/enums/ChatMarker.dart';
 import 'package:flutter_mqtt/abstraction/models/enums/InvitationMessageType.dart';
 import 'package:flutter_mqtt/abstraction/models/enums/MessageType.dart';
 import 'package:flutter_mqtt/abstraction/models/TypingMessage.dart';
+import 'package:flutter_mqtt/abstraction/models/enums/PresenceType.dart';
 import 'package:uuid/uuid.dart';
 
 class MqttChatEventsSender extends ChatEventsSender {
@@ -59,7 +61,13 @@ class MqttChatEventsSender extends ChatEventsSender {
         sendTime: DateTime.now().millisecondsSinceEpoch);
 
     String topic = "invitations/" + username;
-    var js = message.toJson();
     clientHandler.sendPayload(message.toJson().toString(), topic);
   }
+
+  @override
+  void sendPresence(PresenceType presenceType, String myId) {
+    PresenceMessage presenceMessage = PresenceMessage(id: Uuid().v4(), type: presenceType, fromId: myId);
+    String payload = presenceMessage.toJson();
+    clientHandler.sendPayload(payload, "presence/" + myId);
+  }
 }

lib/abstraction/ChatEventsSender.dart

@@ -1,3 +1,6 @@
+import 'package:flutter_mqtt/abstraction/models/PresenceMesssage.dart';
+import 'package:flutter_mqtt/abstraction/models/enums/PresenceType.dart';
+
 import 'models/enums/ChatMarker.dart';
 import 'models/ChatMessage.dart';
 
@@ -11,4 +14,5 @@ abstract class ChatEventsSender {
 
   void sendInvitation(String username, String? invitationId);
   void respondToInvitation(String invitationId, String senderId, bool accept);
+  void sendPresence(PresenceType presenceType, String myId);
 }

lib/db/appdata/AppData.dart

@@ -1,6 +1,7 @@
 import 'package:flutter_mqtt/abstraction/models/enums/ChatMarker.dart';
 import 'package:flutter_mqtt/abstraction/models/enums/InvitationMessageType.dart';
 import 'package:flutter_mqtt/abstraction/models/enums/MessageType.dart';
+import 'package:flutter_mqtt/abstraction/models/enums/PresenceType.dart';
 import 'package:flutter_mqtt/db/appdata/ContactsHandler.dart';
 import 'package:flutter_mqtt/db/appdata/InvitationsHandler.dart';
 import 'package:flutter_mqtt/db/appdata/MessageHandler.dart';
@@ -112,6 +113,10 @@ class AppData {
       ChatApp.instance()!.clientHandler.leaveRoom(contact.roomId);
       ChatApp.instance()!.clientHandler.leaveContactEvents(contact.id);
     }
+    if(user != null) {
+      ChatApp.instance()!.eventsSender.sendPresence(
+          PresenceType.Unavailable, user!.id);
+    }
     ChatApp.instance()!.disconnect();
     await deleteAll();
   }

lib/main.dart

@@ -1,13 +1,48 @@
 import 'package:flutter/material.dart';
+import 'package:flutter_mqtt/abstraction/models/enums/PresenceType.dart';
+import 'package:flutter_mqtt/db/appdata/AppData.dart';
+import 'package:flutter_mqtt/db/database.dart';
+import 'package:flutter_mqtt/global/ChatApp.dart';
 import 'package:flutter_mqtt/ui/screens/startup_page.dart';
 
+import 'abstraction/models/User.dart';
+
 void main() {
   runApp(MyApp());
 }
 
-class MyApp extends StatelessWidget {
+class MyApp extends StatefulWidget {
   // This widget is the root of your application.
   @override
+  _MyAppState createState() => _MyAppState();
+}
+
+class _MyAppState extends State<MyApp> with WidgetsBindingObserver{
+  @override
+  void initState() {
+    WidgetsBinding.instance!.addObserver(this);
+    super.initState();
+  }
+  @override
+  void dispose() {
+    WidgetsBinding.instance!.removeObserver(this);
+    super.dispose();
+  }
+  @override
+  void didChangeAppLifecycleState(AppLifecycleState state) {
+    print('App State = $state');
+
+    DbUser? user = AppData.instance()!.user;
+    if(user != null){
+      if(state == AppLifecycleState.inactive || state == AppLifecycleState.paused){
+        ChatApp.instance()!.eventsSender.sendPresence(PresenceType.Away, user.id);
+      }
+      else if(state == AppLifecycleState.resumed){
+        ChatApp.instance()!.eventsSender.sendPresence(PresenceType.Available, user.id);
+      }
+    }
+  }
+  @override
   Widget build(BuildContext context) {
     return MaterialApp(
       debugShowCheckedModeBanner: false,