Flutter Bloc 不会改变 TextFormField 的初始值

Question

我正在使用 Bloc 库，并注意到在产生新状态后我的 TextFormField initialValue 没有改变。

我的应用比这更复杂，但我做了一个最小的例子。还跟踪它在推送事件后正在更改的状态。

Bloc 应该正确地重建整个小部件。我错过了什么吗？

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

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

enum Event { first }

class ExampleBloc extends Bloc<Event, int> {
  ExampleBloc() : super(0);
  @override
  Stream<int> mapEventToState(Event event) async* {
    yield state + 1;
  }
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: BlocProvider(
        create: (_) => ExampleBloc(),
        child: Builder(
          builder: (contex) => SafeArea(
            child: BlocConsumer<ExampleBloc, int>(
                listener: (context, state) {},
                builder: (context, int state) {
                  developer.log(state.toString());
                  return Scaffold(
                    body: Form(
                      child: Column(
                        children: [
                          TextFormField(
                            autocorrect: false,
                            initialValue: state.toString(),
                          ),
                          RaisedButton(
                            child: Text('Press'),
                            onPressed: () {
                              context.bloc<ExampleBloc>().add(Event.first);
                            },
                          )
                        ],
                      ),
                    ),
                  );
                }),
          ),
        ),
      ),
    );
  }
}

pubspec.yaml

name: form
description: A new Flutter project.
version: 1.0.0+1
environment:
  sdk: ">=2.7.0 <3.0.0"
dependencies:
  flutter:
    sdk: flutter
  bloc: ^6.0.0
  flutter_bloc: ^6.0.0

编辑
正如@chunhunghan 所指出的，添加一个 UniqueKey 可以解决这个问题。我也应该提到我的情况。该应用程序从两个TextFormField 的onChanged 方法发出事件。这会导致窗体重置并删除键盘。自动对焦不起作用，因为有两个 TextFormField wgich 发出事件。

Answer 1

您可以在下面复制粘贴运行完整代码 1 和 2
您可以将UniqueKey() 提供给Scaffold 或TextFormField 以强制重新创建
详情可以参考https://medium.com/flutter/keys-what-are-they-good-for-13cb51742e7d

如果 Element 的 key 与对应的 Widget 的 key 不匹配。这会导致 Flutter 停用这些元素并删除对元素树中元素的引用

解决方案 1：

return Scaffold(
        key: UniqueKey(),
        body: Form(

解决方案 2：

TextFormField(
               key: UniqueKey(),

工作演示

完整代码 1 Scaffold 和 UniqueKey

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

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

enum Event { first }

class ExampleBloc extends Bloc<Event, int> {
  ExampleBloc() : super(0);
  @override
  Stream<int> mapEventToState(Event event) async* {
    yield state + 1;
  }
}

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

  @override
  Widget build(BuildContext context) {
    print("build");
    return MaterialApp(
      home: BlocProvider(
        create: (_) => ExampleBloc(),
        child: Builder(
          builder: (contex) => SafeArea(
            child: BlocConsumer<ExampleBloc, int>(
                listener: (context, state) {},
                builder: (context, int state) {
                  print("state ${state.toString()}");
                  developer.log(state.toString());
                  return Scaffold(
                    key: UniqueKey(),
                    body: Form(
                      child: Column(
                        children: [
                          TextFormField(
                            autocorrect: false,
                            initialValue: state.toString(),
                          ),
                          RaisedButton(
                            child: Text('Press'),
                            onPressed: () {
                              context.bloc<ExampleBloc>().add(Event.first);
                            },
                          )
                        ],
                      ),
                    ),
                  );
                }),
          ),
        ),
      ),
    );
  }
}

完整代码 2 TextFormField 和 UniqueKey

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

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

enum Event { first }

class ExampleBloc extends Bloc<Event, int> {
  ExampleBloc() : super(0);
  @override
  Stream<int> mapEventToState(Event event) async* {
    yield state + 1;
  }
}

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

  @override
  Widget build(BuildContext context) {
    print("build");
    return MaterialApp(
      home: BlocProvider(
        create: (_) => ExampleBloc(),
        child: Builder(
          builder: (contex) => SafeArea(
            child: BlocConsumer<ExampleBloc, int>(
                listener: (context, state) {},
                builder: (context, int state) {
                  print("state ${state.toString()}");
                  developer.log(state.toString());
                  return Scaffold(
                    body: Form(
                      child: Column(
                        children: [
                          TextFormField(
                            key: UniqueKey(),
                            autocorrect: false,
                            initialValue: state.toString(),
                          ),
                          RaisedButton(
                            child: Text('Press'),
                            onPressed: () {
                              context.bloc<ExampleBloc>().add(Event.first);
                            },
                          )
                        ],
                      ),
                    ),
                  );
                }),
          ),
        ),
      ),
    );
  }
}

Answer 2

您不应该仅仅因为要更新TextFormField 的值而重建整个Form，请尝试使用TextEditingController 并更新侦听器上的值。

TextEditingController _controller = TextEditingController();
BlocProvider(
    create: (_) => ExampleBloc(),
    child: Builder(
      builder: (contex) => SafeArea(
        child: BlocListener<ExampleBloc, int>(
            listener: (context, state) {
                _controller.text = state.toString();
            },
            child: Scaffold(
                body: Form(
                  child: Column(
                    children: [
                      TextFormField(
                        controller: _controller,
                        autocorrect: false,
                      ),
                      RaisedButton(
                        child: Text('Press'),
                        onPressed: () {
                          context.bloc<ExampleBloc>().add(Event.first);
                        },
                      )
                    ],
                  ),
                ),
              );
            }),

Answer 3

我也遇到了同样的问题。在添加Unique Key 时，颤动会不断构建小部件，并且我的键盘每次都失焦。我解决它的方法是在TextField的onChanged事件中添加去抖动。

class InputTextWidget extends StatelessWidget {
final Function(String) onChanged;
Timer _debounce;


void _onSearchChanged(String value) {
    if (_debounce?.isActive ?? false) _debounce.cancel();
    _debounce = Timer(const Duration(milliseconds: 2000), () {
      onChanged(value);
    });
  }

@override
  Widget build(BuildContext context) {
         return TextFormField(
          controller: TextEditingController(text: value)
            ..selection = TextSelection.fromPosition(
              TextPosition(offset: value.length),
            ),
          onChanged: _onSearchChanged,
          onEditingComplete: onEditingCompleted,
        );
       }
     }

希望这对使用表单、块和更新表单的人有所帮助。

编辑：虽然添加了去抖动帮助显示了什么。我已将代码更改为更健壮。这是变化。

InputTextWidget（已更改）

class InputTextWidget extends StatelessWidget {
final Function(String) onChanged;
final TextEditingController controller;


void _onSearchChanged(String value) {
    if (_debounce?.isActive ?? false) _debounce.cancel();
    _debounce = Timer(const Duration(milliseconds: 2000), () {
      onChanged(value);
    });
  }

@override
  Widget build(BuildContext context) {
         return TextFormField(
          controller: controller,
          onChanged: _onSearchChanged,
          onEditingComplete: onEditingCompleted,
        );
       }
     }

在我的演讲结束时

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

  @override
  Widget build(BuildContext context) {
    final TextEditingController _controller = TextEditingController();
    return BlocConsumer<SomeBloc,
        SomeState>(
      listenWhen: (previous, current) =>
          previous.name != current.name,
      listener: (context, state) {
        final TextSelection previousSelection = _controller.selection;
        _controller.text = state.name;
        _controller.selection = previousSelection;
      },
      buildWhen: (previous, current) =>
          previous.name != current.name,
      builder: (context, state) => FormFieldDecoration(
        title: "Name",
        child: InputTextWidget(
          hintText: "AWS Certification",
          textInputType: TextInputType.name,
          controller: _controller,
          onChanged: (value) => context
              .read< SomeBloc >()
              .add(SomeEvent(
                  value)),
        ),
      ),
    );
  }
}

此编辑运行良好。

最终编辑：

我在我的 bloc 状态上添加了一个 key? key 并将此密钥传递给小部件。如果我需要再次重绘表单，我将事件中的密钥更改为UniqueKey。这是迄今为止我一起实现 bloc 和 form 的最简单的方法。如果需要解释，请在这里评论，我稍后会补充。