Demo app setup

setup.dart

/// main.dart (the entry point to the demo app)

import 'package:flutter/material.dart';
import 'package:demo_async_test/contrib.dart';
import 'package:demo_async_test/slow.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      initialRoute: '/',
      routes: {
        '/': (context) => MyHomePage(title: 'Flutter Demo Home Page'),
        '/contrib': (context) => ContribScreen(),
        '/slow': (context) => SlowScreen(),
      },
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
            FlatButton(
              child: Text('Check out contrib screen'),
              key: Key('contrib_btn'),
              onPressed: () {
                Navigator.pushNamed(context, '/contrib');
              },
            ),
            FlatButton(
              child: Text('Check out the slow screen'),
              key: Key('slow_btn'),
              onPressed: () {
                Navigator.pushNamed(context, '/slow');
              },
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}

/// contrib.dart (the contrib screen)

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

class ContribScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Help me make more content?'),
        key: Key('contrib_title'),
      ),
      body: Center(
        child: Text('The goal is to let more people have the fun of making stuff'),
      ),
    );
  }
}

/// slow.dart (the slow screen)

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';

class SlowScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Slow Screen'),
      ),
      body: Center(
        child: SlowScreenContent(),
      ),
    );
  }
}

class SlowScreenContent extends StatefulWidget {
  SlowScreenContent({Key key}) : super(key: key);
  @override
  _SlowScreenContent createState() => _SlowScreenContent();
}

class _SlowScreenContent extends State<SlowScreenContent> {
  Future<String> content;
  @override
  void initState() {
    super.initState();
    content = Future.delayed(Duration(seconds: 3), () => 'I am really slo...ow ;)');
  }
  @override
  Widget build(BuildContext context) {
    return FutureBuilder<String>(
      future: content,
      builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
        switch (snapshot.connectionState) {
          case ConnectionState.none:
            return Text('Not started');
          case ConnectionState.active:
            return Text('Active');
          case ConnectionState.waiting:
            return Text('Awaiting result...');
          case ConnectionState.done:
            if (snapshot.hasError)
              return Text('Error: ${snapshot.error}');
            return Text('Result: ${snapshot.data}', key: Key('slow_content'));
        }
        return Text('Unknown state :(');
      },
    );
  }
}