Bloc パターンで State を更新する際に何が比較されているのか確認するサンプル。

state_compare_sample.dart

import 'package:flutter/material.dart';
import 'package:bloc/bloc.dart';
import 'package:equatable/equatable.dart';
import 'package:flutter_bloc/flutter_bloc.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @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'),
    );
  }
}

// MARK: - Entity

class CountEntity extends Equatable {
  final int count;
  final DateTime time;

  const CountEntity(this.count, this.time);

  // NOTE: やっぱり props に何も指定しなければ
  // 当たり前だが、型のみが評価されてしまうため、メンバーが変更されても考慮されない.
  @override
  List<Object> get props => [];
  //List<Object> get props => [count, time];
}

// MARK: - Event

abstract class CounterEvent extends Equatable {
  const CounterEvent();

  @override
  List<Object> get props => [];
}

class CounterIncrement extends CounterEvent {
  const CounterIncrement();

  @override
  List<Object> get props => [];
}

// MARK: - State

abstract class CounterState extends Equatable {
  const CounterState();

  @override
  List<Object> get props => [];
}

class CounterInitState extends CounterState {
  final CountEntity entity;

  const CounterInitState(this.entity);

  @override
  List<Object> get props => [entity];
}

class CounterUpdatedState extends CounterState {
  final CountEntity entity;

  const CounterUpdatedState(this.entity);

  @override
  List<Object> get props => [entity];
}

// MARK: - BLoC

class CounterBloc extends Bloc<CounterEvent, CounterState> {
  CounterBloc();

  @override
  CounterState get initialState => CounterInitState(CountEntity(0, DateTime.now()));

  @override
  Stream<CounterState> mapEventToState(CounterEvent event) async* {
    if (event is CounterIncrement) {
      if (state is CounterInitState) {
        final _state = state as CounterInitState;
        yield CounterUpdatedState(CountEntity(_state.entity.count + 1, DateTime.now()));
      } else if (state is CounterUpdatedState) {
        final _state = state as CounterUpdatedState;
        yield CounterUpdatedState(CountEntity(_state.entity.count + 1, DateTime.now()));
      }
    }
  }
}

// MARK: - Screen

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

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  final CounterBloc _bloc = CounterBloc();

  @override
  void dispose() {
    _bloc.close();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: BlocBuilder(
        bloc: _bloc,
        builder: (context, state) {
          if (state is CounterInitState) {
            return Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text('You have pushed the button this many times:',),
                  Text(
                    '${state.entity.count}',
                    style: Theme.of(context).textTheme.headline4,
                  ),
                ],
              ),
            );
          }
          if (state is CounterUpdatedState) {
            return Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: <Widget>[
                  Text(
                    '${state.entity.count}',
                    style: Theme.of(context).textTheme.headline4,
                  ),
                  Text(
                    'last updated ${state.entity.time}',
                    style: TextStyle(color: Colors.grey),
                  ),
                ],
              ),
            );
          }

          return Center(
            child: Text('Unkown state.'),
          );
        },
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: () => _bloc.add(CounterIncrement()),
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ),
    );
  }
}