How to keep the App always logged in with Firebase

According to the Manage Users on Firebase documentation, the recommended way to identify the user connected is to call the getCurrentUser() method. If no user is logged in, getCurrentUser() returns a null value.

Example:

FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
if (user != null) {
    // Usuário está logado
} else {
    // usuário não está logado
}