今天要教大家使用Bloc的BlocConsumer，讓狀態改變，但我們沒有想要更新畫面的時候，就可以用Listener去執行特定的事情或是顯示出彈跳視窗，我會繼續將連兩天的Flutter Package - Bloc（一）及Flutter Package - Bloc（二）繼續延伸，讓大家更能夠了解Bloc的應用

修改bloc_screen.dart檔案
將BlocProvider改為BlocConsumer，並在裡面加入listener監聽State

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

import 'counter_management_bloc.dart';

class BlocScreen extends StatelessWidget {
  const BlocScreen({Key? key}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(title: const Text('Counter')),
        body: BlocProvider(
          create: (_) => CounterManagementBloc(),
          child: BlocConsumer<CounterManagementBloc, CounterManagementState>(listener: (context, state) async {
            if (state is CounterManagementDecreasedFailure) {
              await showDialog<String>(
                context: context,
                builder: (BuildContext context) {
                  return AlertDialog(content: Text(state.reason));
                },
              );
            }
            if (state is CounterManagementIncreasedFailure) {
              await showDialog<String>(
                context: context,
                builder: (BuildContext context) {
                  return AlertDialog(content: Text(state.reason));
                },
              );
            }
          }, builder: (context, state) {
            return Center(
              child: Column(
                mainAxisAlignment: MainAxisAlignment.center,
                children: [
                  Row(
                    crossAxisAlignment: CrossAxisAlignment.center,
                    mainAxisAlignment: MainAxisAlignment.spaceAround,
                    children: [
                      ElevatedButton(
                        onPressed: () {
                          context.read<CounterManagementBloc>().add(CounterManagementDecreased());
                        },
                        child: const Icon(Icons.remove),
                      ),
                      Text(state.count.toString()),
                      ElevatedButton(
                        onPressed: () {
                          context.read<CounterManagementBloc>().add(CounterManagementIncreased());
                        },
                        child: const Icon(Icons.add),
                      ),
                    ],
                  ),
                  const SizedBox(
                    height: 20,
                  ),
                  ElevatedButton(
                    onPressed: () {
                      context.read<CounterManagementBloc>().add(CounterManagementReset());
                    },
                    child: const Text("reset"),
                  ),
                  const SizedBox(
                    height: 100,
                  ),
                ],
              ),
            );
          }),
        ));
  }
}