BlocListener仅执行一次

Question

我正在重新编写一个非常简单的应用程序来计算平均值，但是我很难使用BLoC模式。

我的目标是在用户未在TextField中键入成绩时显示AlertDialog。这只能工作一次，但是当我再次尝试时，它什么也没显示。

我该如何解决？

我无法为BLoC构建器分配“未来”，因为它要求我提供小部件。

图片1：

图片2：

代码：

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

import '../shared/custom_card.dart';

import '../bloc/average_bloc.dart';

class ArithmeticAverageScreen extends StatefulWidget {
  @override
  _ArithmeticAverageScreenState createState() => _ArithmeticAverageScreenState();
}


class _ArithmeticAverageScreenState extends State<ArithmeticAverageScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('arithmetic_average_title').tr(),
      ),
      body: BlocConsumer<AverageBloc, AverageState>(
        listener: (context, state) {
          if (state is AverageError) {
            return errorDialog(context, state.message);
          }
        },
        builder: (context, state) {
          return buildListViewWithCards(context);   
        },
      )
    );
  }
}

Future errorDialog(BuildContext context, message) {
  return showDialog(
    context: context,
    child: AlertDialog(
      title: Text(message)
    )
  );
}

Widget buildListViewWithCards(BuildContext context) {
  TextEditingController _textFieldController = TextEditingController();

  return Container(
    padding: EdgeInsets.all(20.0),
    child: ListView(
      children: <Widget>[
        CustomCard(
          child: Column(
            children: <Widget>[
              ListTile(
                leading: Icon(Icons.help),
                title: Text('arithmetic_average_help').tr(),
                subtitle: Text('arithmetic_average_help_content').tr(),
              )
            ],
          ),
        ),
        SizedBox(height: 16.0),
        CustomCard(
          child: Container(
            padding: EdgeInsets.symmetric(horizontal: 16.0),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                Text('arithmetic_average_your_grades', style: Theme.of(context).textTheme.headline5).tr(),
                SizedBox(height: 16.0),
                Text('arithmetic_average_type_grades', style: Theme.of(context).textTheme.headline6).tr(),
                SizedBox(height: 16.0),
                Row(
                  children: <Widget>[
                    Container(
                      width: 60.0,
                      child: TextField(
                        controller: _textFieldController,
                        decoration: InputDecoration(
                          labelText: 'arithmetic_average_textfield_hint'.tr(),
                          hintText: '5'
                        ),
                      ),
                    ),
                    SizedBox(width: 16.0),
                    RaisedButton(
                      onPressed: () {
                        submitGrade(context, _textFieldController.text);
                      },
                      child: Text('arithmetic_average_add_button').tr(),
                      color: Colors.teal[300],
                      textColor: Colors.white,
                    )
                  ],
                )
              ],
            ),
          )
        ),
        SizedBox(height: 16.0),
        CustomCard(
          child: Container(
            padding: EdgeInsets.symmetric(horizontal: 16.0),
            child: Column(
              crossAxisAlignment: CrossAxisAlignment.start,
              children: <Widget>[
                Text('arithmetic_average_your_average', style: Theme.of(context).textTheme.headline5).tr(),
                SizedBox(height: 16.0),
                Center(
                  child: Text('???', style: Theme.of(context).textTheme.headline4)
                )
              ],
            )
          )
        )
      ],
    )
  );
}

void submitGrade(BuildContext context, String average) {
  final averageBloc = BlocProvider.of<AverageBloc>(context);
  averageBloc.add(GetArithmeticAverage(average));
}