Add Online Offline Status in Flutter App Like Whatsapp using Firebase but how i Handle without internet

Firestore has no built-in capability to write something in the database after the client has disconnected. In fact, most databases don't have such a capability.

One exception is Firebase's other database: the Realtime Database, which has so-called onDisconnect handlers, which are delayed write instructions that you to the database when you are connection, and which the database then executes once it detects that the connection is gone.

You can combine the Realtime Database with Firestore as shown in the links below.

See:

• The FlutterFire documentation on onDisconnect handlers.
• The Firebase documentation on building a presence system with the Realtime Database.
• The Firebase documentation on connecting Realtime Database and Firestore to get presence information into Firestore too.