main.dart

bool isLoggedIn = false;

  void onLoginStatusChanged(bool isLoggedIn) {
    setState(() {
      this.isLoggedIn = isLoggedIn;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text("Facebook Login"),
        ),
        body: Container(
          child: Center(
            child: isLoggedIn
                ? Text("Logged In")
                : RaisedButton(
                    child: Text("Login with Facebook"),
                    onPressed: () => initiateFacebookLogin(),
                  ),
          ),
        ),
      ),
    );
  }