firebase-auth-2-myhomepagestate-1.dart

class _MyHomePageState extends State<MyHomePage> {
  final FirebaseAuth firebaseAuth = FirebaseAuth.instance;
  UserCredential user;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[
          Builder(builder: (BuildContext context) {
            return FlatButton(
              child: const Text('Sign out'),
              textColor: Theme.of(context).buttonColor,
              onPressed: () async {
                final User user = await firebaseAuth.currentUser;
                if (user == null) {
                  Scaffold.of(context).showSnackBar(const SnackBar(
                    content: Text('No one has signed in.'),
                  ));
                  return;
                }
                signOut();
              },
            );
          })
        ],
      ),
      body: Center(
          child: Column(children: [
            FlatButton(onPressed: () {signInWithGitHub();}, child: Text("Sign In With GitHub")),
            Text((user != null) ? user.user.displayName : "Not logged in"),
          ],)
      ),
    );
  }
}