Implement realtime online/offline status with flutter and firebase

Hy, what is the best way to show in an app if the user is online or offline?

Frontend -> Flutter

Backend -> Firestore Cloud and Firebase Auth.

I have a collection of users in firestore that contains documents. Each document is a user and contain "status" field. In flutter i can update this field every time that user sign in or log out but if you close the app it is not updated.

You can extend your statefulWidget State class with WidgetsBindingObserver like

class _HomePageState extends State<HomePage>
    with WidgetsBindingObserver

and initState method add WidgetsBinding.instance.addObserver(this);.

@override
  void initState() {
    super.initState();
    WidgetsBinding.instance.addObserver(this);
  }

Later overide didChangeAppLifecycleState method

@override
  void didChangeAppLifecycleState(AppLifecycleState state) {
    if (state == AppLifecycleState.resumed)
      //TODO: set status to online here in firestore
    else
      //TODO: set status to offline here in firestore
  }

IT CAN DONE BY WidgetsBindingObserver();

class _HomeState extends State<Home> with WidgetsBindingObserver {...}

initialize it first

@override
void initState() {
super.initState();
WidgetsBinding.instance!.addObserver(this);
}

After add this function to listen for app state didChangeAppLifecycleState()

String? changes;

@override
void didChangeAppLifecycleState(AppLifecycleState state) {
super.didChangeAppLifecycleState(state);

final isBg = state == AppLifecycleState.paused;
final isClosed = state == AppLifecycleState.detached;
final isScreen = state == AppLifecycleState.resumed;

isBg || isScreen == true || isClosed == false
    ? setState(() {
      // SET ONLINE
    })
    : setState(() {
      //SET  OFFLINE

    });
print('CHANGES IS : $changes ');

}

String? changes Contains Your app State! Be Happy You Can what you want , This can notify Online status like Whatsapp Messenger!

MyCode :

    isBg || isScreen == true || isClosed == false
    ? setState(() {
      changes = "User is online"
    })
    : setState(() {
      changes = "User is Offline"
    });
    print('CHANGES IS : $changes ');