check user online if user has internet connection using firebase

Question

I want to make an application in which if user is connected to internet it must show as an online user on other devices using firebase. what should be appropriate way for that ?

Answer 1

I recommend using Firebase's built-in onDisconnect() method. It enables you to predefine an operation that will happen as soon as the client becomes disconnected.

See Firebase documentation.

You can also detect the connection state of the user. For many presence-related features, it is useful for your app to know when it is online or offline. Firebase Realtime Database provides a special location at /.info/connected which is updated every time the Firebase Realtime Database client's connection state changes. Here is an example also from the official documentation:

DatabaseReference connectedRef = FirebaseDatabase.getInstance().getReference(".info/connected");
    connectedRef.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot snapshot) {
            boolean connected = snapshot.getValue(Boolean.class);
            if (connected) {
                System.out.println("connected");
            } else {
                System.out.println("not connected");
            }
        }

        @Override
        public void onCancelled(DatabaseError error) {
            System.err.println("Listener was cancelled");
        }
});

Answer 2

You can have a list in your firebase of all online users, so when the user opens the app, you will immediately add his Id to the list. Then, if you want to check if the user is online, just check if his Id is in the list.

You can also add isOnline variable to the user's reference in your database.