[flutter-chat-demo]main2.dart

Future < Null > handleSignOut() async {
    this.setState(() {
        isLoading = true;
    });

    await FirebaseAuth.instance.signOut();
    await googleSignIn.disconnect();
    await googleSignIn.signOut();

    this.setState(() {
        isLoading = false;
    });

    Navigator.of(context).pushAndRemoveUntil(
        MaterialPageRoute(builder: (context) => MyApp()),
        (Route < dynamic > route) => false);
}