Handling asynchronous state with a FutureBuilder widget

jokestate.dart

class JokePageState extends State<JokePage> {
  Future<String> response;

  initState() {
    super.initState();
    response = http.read(dadJokeApi, headers: httpHeaders);
  }

  Widget build(BuildContext context) {
    return new Scaffold(
      body: new Center(
        child: new FutureBuilder<String>(
          future: response,
          builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
            switch (snapshot.connectionState) {
              case ConnectionState.none:
                return const Icon(Icons.sync_problem);
              case ConnectionState.waiting:
              case ConnectionState.active:
                return const CircularProgressIndicator();
              case ConnectionState.done:
                final decoded = json.decode(snapshot.data);
                if (decoded['status'] == 200) {
                  return new Text(decoded['joke']);
                } else {
                  return const Icon(Icons.error);
                }
            }
          },
        ),
      ),
    );
  }
}