The Counter app with const constructors

const_counter_app

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  const MyApp({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) => MaterialApp(
        theme: ThemeData(
          primarySwatch: Colors.green,
          visualDensity: VisualDensity.adaptivePlatformDensity,
        ),
        home: const MyHomePage(title: 'Flutter Demo Home Page'),
      );
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key key, this.title}) : super(key: key);
  final String title;

  @override
  State createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  _MyHomePageState() : bloc = Bloc();
  final Bloc bloc;

  @override
  Widget build(BuildContext context) => Scaffold(
        appBar: AppBar(
          title: Text(widget.title),
        ),
        body: Center(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              const Text(
                'You have clicked the button this many times:',
              ),
              Text(
                bloc.data,
                style: Theme.of(context).textTheme.headline4,
              ),
            ],
          ),
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () {
            setState(bloc.onPressed);
          },
          tooltip: 'Increment',
          child: const Icon(Icons.add),
        ),
      );
}

/// A Business Logic Component
/// This BLoC relays functionality between your app's data source
/// and its interface. It's your app's event handler (i.e. your app's API).
///
/// It contains all the 'mutable' elements for the counter app.
///
class Bloc {
  Bloc() {
    _counter = 0;
  }
  int _counter;

  String get data => _counter.toString();

  void onPressed() => _counter++;
}