Flutter 为什么我的步进器一直产生空输出？颤振

我正在尝试学习如何使用stepper小部件，但我面临一个问题。目前在我的步骤3中，它应该显示步骤1和2中的所有用户输入。两者的输出均为空。为什么会这样

这是我的代码：

import 'package:flutter/services.dart';

class StoreManagement extends StatefulWidget {
static const String pageId = 'StoreManagement';
@override
_StoreManagementState createState() => _StoreManagementState();
}

class _StoreManagementState extends State<StoreManagement> {
List<Step> _steps;
int _current;
TextEditingController _name;
TextEditingController _age;
String _nameDisplay;
String _ageDisplay;

void _stepContinue() {
 setState(() {
   _current++;
   if (_current >= _steps.length) _current = _steps.length - 1;
   if (_current == 2) {
     _ageDisplay = _age.text;
     _nameDisplay = _name.text;
   }
 });
}

void _stepCancel() {
 setState(() {
   _current--;
   if (_current < 0) _current = 0;
 });
}

void _stepTap(int index) {
 setState(() {
   _current = index;
 });
}

@override
void initState() {
 _name = TextEditingController();
 _age = TextEditingController();
 _current = 0;
 _steps = <Step>[
   Step(
     isActive: true,
     title: Text('Enter your name'),
     content: TextField(
       controller: _name,
       decoration: InputDecoration(labelText: 'Enter your Name'),
     ),
   ),
   Step(
     isActive: true,
     title: Text('Enter your age'),
     content: TextField(
       keyboardType: TextInputType.number,
       controller: _age,
       decoration: InputDecoration(
         labelText: 'Enter your Age',
       ),
     ),
   ),
   Step(
     isActive: true,
     title: Text('Step 3'),
     content: Column(
       children: <Widget>[
         Text('You have entered: '),
         Text('Your name is : ${_nameDisplay}'),
         Text('Your age is : ${_ageDisplay}'),
       ],
     ),
   )
 ];
 super.initState();
}

@override
Widget build(BuildContext context) {
 return Scaffold(
   body: Stepper(
     steps: _steps,
     currentStep: _current,
     type: StepperType.vertical,
     onStepCancel: _stepCancel,
     onStepContinue: _stepContinue,
     onStepTapped: _stepTap,
   ),
 );
}
}

import'package:flatter/services.dart'；
类StoreManagement扩展了StatefulWidget{
静态常量字符串pageId='StoreManagement'；
@凌驾
_StoreManagementState createState（）=>\u StoreManagementState（）；
}
类_StoreManagementState扩展状态{
列出步骤；
int_电流；
TextEditingController\u名称；
文本编辑控制器；
字符串显示；
字符串显示；
void _stepContinue（）{
设置状态（）{
_电流++；
如果（\u current>=\u steps.length）\u current=\u steps.length-1；
如果（_current==2）{
_ageDisplay=\u age.text；
_名称显示=_name.text；
}
});
}
作废_步骤取消（）{
设置状态（）{
_当前--；
如果（_电流<0）_电流=0；
});
}
void _stepTap（整数索引）{
设置状态（）{
_电流=指数；
});
}
@凌驾
void initState（）{
_name=TextEditingController（）；
_年龄=文本编辑控制器（）；
_电流=0；
_步骤=[
台阶(
是的，
标题：文本（“输入您的姓名”），
内容：TextField(
控制器：_名称，
装饰：输入装饰（标签文本：“输入您的姓名”），
),
),
台阶(
是的，
标题：文本（“输入您的年龄”），
内容：TextField(
键盘类型：TextInputType.number，
控制员：_年龄，
装饰：输入装饰(
labelText:“输入您的年龄”，
),
),
),
台阶(
是的，
标题：文本（“步骤3”），
内容：专栏(
儿童：[
Text（'您已输入：'），
Text（'您的名字是：${u namesplay}'），
Text（'您的年龄是：${u ageDisplay}'），
],
),
)
];
super.initState（）；
}
@凌驾
小部件构建（构建上下文）{
返回脚手架(
机身：步进电机(
步骤：_步骤，
当前步骤：_当前，
类型：StepperType.vertical，
onStepCancel:\u步骤取消，
onStepContinue:_stepContinue，
OnStepTap:_stepTap，
),
);
}
}

---

我曾尝试在步进机外打印值，但似乎有效。不太明白为什么它在第三步不起作用。

您可以使用函数返回步骤
您可以复制粘贴运行下面的完整代码
代码片段

Widget build(BuildContext context) {
    return Scaffold(
      body: Stepper(
        steps: buildStep(),

...

List<Step> buildStep() {
_steps = <Step>[
  Step(
    isActive: true,
    title: Text('Enter your name'),
    content: TextField(
      controller: _name,
      decoration: InputDecoration(labelText: 'Enter your Name'),
    ),
  ),
  Step(
    isActive: true,
    title: Text('Enter your age'),
    content: TextField(
      keyboardType: TextInputType.number,
      controller: _age,
      decoration: InputDecoration(
        labelText: 'Enter your Age',
      ),
    ),
  ),
  Step(
    isActive: true,
    title: Text('Step 3'),
    content: Column(
      children: <Widget>[
        Text('You have entered: '),
        Text('Your name is : ${_nameDisplay}'),
        Text('Your age is : ${_ageDisplay}'),
      ],
    ),
  )
];

return _steps;
}

小部件构建（构建上下文）{
返回脚手架(
机身：步进电机(
步骤：buildStep（），
...
列表buildStep（）{
_步骤=[
台阶(
是的，
标题：文本（“输入您的姓名”），
内容：TextField(
控制器：_名称，
装饰：输入装饰（标签文本：“输入您的姓名”），
),
),
台阶(
是的，
标题：文本（“输入您的年龄”），
内容：TextField(
键盘类型：TextInputType.number，
控制员：_年龄，
装饰：输入装饰(
labelText:“输入您的年龄”，
),
),
),
台阶(
是的，
标题：文本（“步骤3”），
内容：专栏(
儿童：[
Text（'您已输入：'），
Text（'您的名字是：${u namesplay}'），
Text（'您的年龄是：${u ageDisplay}'），
],
),
)
];
返回步骤；
}

工作演示

完整代码

import 'package:flutter/material.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(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: StoreManagement(),
    );
  }
}

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

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,
        tooltip: 'Increment',
        child: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}


class StoreManagement extends StatefulWidget {
  static const String pageId = 'StoreManagement';
  @override
  _StoreManagementState createState() => _StoreManagementState();
}

class _StoreManagementState extends State<StoreManagement> {
  List<Step> _steps;
  int _current;
  TextEditingController _name;
  TextEditingController _age;
  String _nameDisplay;
  String _ageDisplay;

  void _stepContinue() {
    setState(() {
      _current++;
      if (_current >= _steps.length) _current = _steps.length - 1;
      print('current ${_current}');
      if (_current == 2) {
        _ageDisplay = _age.text;
        print('_ageDisplay ${_ageDisplay}');
        _nameDisplay = _name.text;
        print('_nameDisplay ${_nameDisplay}');
      }
    });
  }

  void _stepCancel() {
    setState(() {
      _current--;
      if (_current < 0) _current = 0;
    });
  }

  void _stepTap(int index) {
    setState(() {
      _current = index;
    });
  }

  @override
  void initState() {
    _name = TextEditingController();
    _age = TextEditingController();
    _current = 0;

    super.initState();
  }

  List<Step> buildStep() {
    _steps = <Step>[
      Step(
        isActive: true,
        title: Text('Enter your name'),
        content: TextField(
          controller: _name,
          decoration: InputDecoration(labelText: 'Enter your Name'),
        ),
      ),
      Step(
        isActive: true,
        title: Text('Enter your age'),
        content: TextField(
          keyboardType: TextInputType.number,
          controller: _age,
          decoration: InputDecoration(
            labelText: 'Enter your Age',
          ),
        ),
      ),
      Step(
        isActive: true,
        title: Text('Step 3'),
        content: Column(
          children: <Widget>[
            Text('You have entered: '),
            Text('Your name is : ${_nameDisplay}'),
            Text('Your age is : ${_ageDisplay}'),
          ],
        ),
      )
    ];

    return _steps;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Stepper(
        steps: buildStep(),
        currentStep: _current,
        type: StepperType.vertical,
        onStepCancel: _stepCancel,
        onStepContinue: _stepContinue,
        onStepTapped: _stepTap,
      ),
    );
  }
}

导入“包装：颤振/材料.省道”；
void main（）=>runApp（MyApp（））；
类MyApp扩展了无状态小部件{
//此小部件是应用程序的根。
@凌驾
小部件构建（构建上下文）{
返回材料PP(
标题：“颤振演示”，
主题：主题数据(
//这是应用程序的主题。
//
//尝试使用“flutter run”运行应用程序。您将看到
//应用程序有一个蓝色工具栏。然后，在不退出应用程序的情况下，重试
//将下面的primarySwatch更改为Colors.green，然后调用
//“热重新加载”（在运行“颤振运行”的控制台中按“r”，
//或者只需将更改保存到颤振IDE中的“热重新加载”。
//请注意，计数器没有重置回零；应用程序
//未重新启动。
主样本：颜色。蓝色，
),
主页：StoreManagement（），
);
}
}
类MyHomePage扩展StatefulWidget{
MyHomePage（{Key，this.title}）：超级（Key:Key）；
//此小部件是应用程序的主页。它是有状态的，表示
//它有一个状态对象（定义如下），其中包含影响
//看起来怎么样。
//此类是状态的配置。它保存值（在此
//案例名称）由家长（在本例中为应用程序小部件）提供，以及
//由State的build方法使用。小部件子类中的字段包括
//始终标记为“最终”。
最后的字符串标题；
@凌驾
_MyHomePageState createState（）=>\u MyHomePageState（）；
}
类_MyHomePageState扩展状态{
int _计数器=0；
void _incrementCounter（）{
设置状态（）{
//这个对setState的调用告诉颤振框架，某些东西
//已在此状态下更改，这将导致它重新运行下面的生成方法
//以便显示能够反映更新的值。如果我们更改
//_计数器，而不调用setState（），则生成方法将不可用
//再打一次电话，似乎什么也没发生。
_计数器++；
});
}
@凌驾
小部件构建（构建上下文）{
//每次调用setState时都会重新运行此方法，例如，按done
//通过上面的_incrementCounter方法。
//
//对颤振框架进行了优化，以制定重新运行的构建方法
//快速，这样你就可以重建任何需要更新的东西
//而不是必须单独更改小部件的实例。
返回脚手架(
appBar:appBar(
//在这里，我们从MyHomePage对象中获取由创建的值
//App.build方法，并使用它设置