flutter_codex_01.dart

import 'package:flutter/material.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.yellow,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  bool logged = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Flutter Codex'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            RaisedButton(
              child: Text('Login'),
              onPressed: () {},
              color: Colors.blue[300],
            ),
            RaisedButton(
              child: Text('Logout'),
              onPressed: () {},
              color: Colors.red[300],
            ),
            SizedBox(
              height: 20,
            ),
            logged
                ? Text(
                    'The user is logged!',
                    style: TextStyle(
                      color: Colors.blue,
                    ),
                  )
                : Text(
                    'The user is not logged!',
                    style: TextStyle(
                      color: Colors.red,
                    ),
                  ),
          ],
        ),
      ),
    );
  }
}