import 'package:flutter/foundation.dart' show compute;
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.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  Animal _animal;
  int _count = 0;

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'Current animal is:',
            ),
            Text(
              '$_animal',
              style: Theme.of(context).textTheme.headline4,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () async {
          _count++;
          _animal = await compute(AnimalManage.getAnimal, _count % 3);
          print('current _animal = $_animal, hashCode = ${_animal.hashCode}');
          for (Animal animal in Animal.values) {
            print('$animal : ${animal.hashCode}');
          }
          setState(() {});
        },
        tooltip: 'add',
        child: Icon(Icons.add),
      ),
    );
  }
}

enum Animal {
  dog,
  fish,
  cat,
}

class AnimalManage {
  static Animal getAnimal(int arg) {
    for (Animal animal in Animal.values) {
      print('setAnimal: $animal, hashCode : ${animal.hashCode}');
    }
    return Animal.values[arg];
  }
}