Flutter 颤振-自定义小部件-如何从

这是我遇到的问题的一个简单例子。给出以下示例，如何从类外获取“counter”的值

class Counter extends StatefulWidget {
  @override
  _CounterState createState() => _CounterState();
}

class _CounterState extends State<Counter> {
  int counter = 0;
  void increaseCount() {
    setState(() => this.counter++);
    print("New count = $counter");
  }

  Widget build(context) {
    return new RaisedButton(
      onPressed: increaseCount,
      child: new Text('Tap To Add'),
    );
  }
}

类计数器扩展StatefulWidget{
@凌驾
_CounterState createState（）=>\u CounterState（）；
}
类_countstate扩展状态{
int计数器=0；
无效增量计数（）{
setState（（）=>this.counter++）；
打印（“新计数=$计数器”）；
}
小部件构建（上下文）{
返回新的RaisedButton(
onPressed:增加计数，
子项：新文本（“点击添加”），
);
}
}

在flatter中，您通常要做的是传递回调函数，在该函数中您可以传递所需的值，例如

class Counter extends StatefulWidget {
  // you can use a callback function
  final ValueSetter<int> callback;

  Counter({this.callback});

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

class _CounterState extends State<Counter> {
  int counter = 0;
  void increaseCount() {
    setState(() => this.counter++);
    print("New count = $counter");
    // Here you can pass the value
    widget.callback(this.counter);
  }

  Widget build(context) {
    return new RaisedButton(
      onPressed: increaseCount,
      child: new Text('Tap To Add'),
    );
  }
}

这是我所知道的最简单的方法，也可以使用其他一些模式，如bloc或其他模式。

---

希望能有所帮助。

您可以使用如下GlobalKey：

类计数器扩展StatefulWidget{
@凌驾
最终globalKey=globalKey（）；
@凌驾
_CounterState createState（）=>\u CounterState（）；
}
类_countstate扩展状态{
int计数器=0；
无效增量计数（）{
设置状态（（）=>计数器++）；
打印（“新计数=$计数器”）；
}
@凌驾
小部件构建（上下文）{
返回上升按钮(
onPressed:增加计数，
子项：文本（“点击添加”），
);
}
}

然后按如下方式访问计数器：

计数器计数器=计数器（）；
int count=counter.globalKey.currentState.counter；

警告：这是不推荐的

您正在从一个简单的、包含的状态过渡到多个小部件之间共享的状态。有几种更好的方法来解决这个问题。有关更多信息和更好的解决问题的方法，请访问。

这只是一个示例（概念验证），用于演示我想要实现的目标。我只是想让小部件存储它的值，并在我需要时将其提供给我（即更新数据）。另一种选择是由主程序存储值，但我认为这并不理想

以下内容似乎有效。为了简单地获得计数器的值，我似乎要做很多事情。我希望有一个更简单的方法。代码如下：

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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

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

class _MyHomePageState extends State<MyHomePage> {
  CounterWithState _counterWithState =
      CounterWithState(iCounter: 0, isAllowedChange: true);
  FloatingActionButton _fab;
  final _scaffoldKey = GlobalKey<ScaffoldState>();
  @override
  void initState() {
    super.initState();
    _fab = FloatingActionButton(
      onPressed: _showSnackbar,
      tooltip: 'Press to show Counter',
      child: Icon(Icons.info),
    );
  }

  _showSnackbar() {
    _scaffoldKey.currentState.showSnackBar(SnackBar(
        backgroundColor: Colors.blue,
        content:
            Text("Current value of Counter is ${_counterWithState.iCounter}")));
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: Text(widget.title),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            _counterWithState.getCounterWidget(),
          ],
        ),
      ),
      floatingActionButton: _fab,
    );
  }
}

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  final String sTitle = 'Flutter Counter-With-State Demo';
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: sTitle,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: sTitle),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  CounterWithState _counterWithState;
  FloatingActionButton _fab;
  int _iCounterOriginal = 99;
  RaisedButton _raisedButton;
  SizedBox _sizedBox;
  final _scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  void initState() {
    super.initState();
    _fab = FloatingActionButton(
      onPressed: _showSnackbar,
      tooltip: 'Press to show Counter',
      child: Icon(Icons.info),
    );
    _raisedButton = RaisedButton(
        child: const Text('Update'),
        color: Theme.of(context).accentColor,
        elevation: 4.0,
        splashColor: Colors.blueGrey,
        onPressed: () {
          _iCounterOriginal = _counterWithState.iCounter;
          _counterWithState = null;
          _getCounterWithState(context);
          setState(() {});
        });
    _sizedBox = SizedBox(height: _raisedButton.height);
  }

  fnCounterChanged(int iCounter) {
    setState(() {});
  }

  _showSnackbar() {
    _scaffoldKey.currentState.showSnackBar(SnackBar(
        backgroundColor: Colors.blue,
        content:
            Text("Current value of Counter is ${_counterWithState.iCounter}")));
  }

  @override
  Widget build(BuildContext context) {
    _counterWithState = _counterWithState != null
        ? _counterWithState
        : _getCounterWithState(context);
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: Text(widget.title),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            _counterWithState.getCounterWidget(),
            _getUpdateButton(context),
          ],
        ),
      ),
      floatingActionButton: _fab,
    );
  }

  Widget _getUpdateButton(BuildContext context) {
    return _counterWithState == null ||
            _counterWithState.iCounter == _iCounterOriginal
        ? _sizedBox
        : _raisedButton;
  }

  CounterWithState _getCounterWithState(context) {
    if (_counterWithState == null)
      _counterWithState = CounterWithState(
          iCounter: _iCounterOriginal,
          isAllowedChange: true,
          fnNotifyChange: fnCounterChanged);
    return _counterWithState;
  }
}

导入“包装：颤振/材料.省道”；
导入“计数器状态.省道”；
void main（）=>runApp（MyApp（））；
类MyApp扩展了无状态小部件{
@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(
主样本：颜色。蓝色，
),
主页：MyHomePage（标题：“颤振演示主页”），
);
}
}
类MyHomePage扩展StatefulWidget{
MyHomePage（{Key，this.title}）：超级（Key:Key）；
最后的字符串标题；
@凌驾
_MyHomePageState createState（）=>\u MyHomePageState（）；
}
类_MyHomePageState扩展状态{
抗衡状态=
计数器状态（i计数器：0，isAllowedChange:true）；
浮动操作按钮_fab；
最终_scaffoldKey=GlobalKey（）；
@凌驾
void initState（）{
super.initState（）；
_fab=浮动操作按钮(
按下按钮：_showSnackbar，
工具提示：“按此键可显示计数器”，
子：图标（Icons.info），
);
}
_showSnackbar（）{
_scaffoldKey.currentState.showSnackBar（SnackBar(
背景颜色：Colors.blue，
内容：
Text（“计数器的当前值为${u counterWithState.iCounter}”）；
}
@凌驾
小部件构建（构建上下文）{
返回脚手架(
钥匙：_scaffoldKey，
appBar:appBar(
标题：文本（widget.title），
),
正文：中(
子：列(
mainAxisAlignment:mainAxisAlignment.center，
儿童：[
_counterWithState.getCounterWidget（），
],
),
),
浮动操作按钮：_fab，
);
}
}

导入“包装：颤振/材料.省道”；
阶级对抗状态{
国际货币基金组织；
CounterWithStateInternal _CounterWithStateInternal；
fnDataChanged（int iNewCounter）{
_i计数器=不计数器；
debugPrint（“CounterWithState:New value=$\u iCounter”）；
}
CounterWithStateInternalGetCounterWidget（）{
返回(内部状态);；
}
计数器状态（{@required iCounter，@required bool isAllowedChange}）{
_i计数器=i计数器；
_counterWithStateInternal=counterWithStateInternal(
GlobalKey（），this.\u i计数器，isAllowedChange，fnDataChanged）；
}
获取iCounter=>\u iCounter；
}
类CounterWithStateInternal扩展StatefulWidget{
最终国际数学家；
最后一次bool-tfAllowChange；
最终功能改变；
反陈述内部(
Key Key、this.iCounter、this.tfAllowChange、this.fndatachange）
：super（key:key）；
@凌驾
CounterWithStateMain createState（）=>CounterWithStateMain（）；
}
类CounterWithStateMain扩展状态{
int _i计数器=0；
@凌驾
initState（）{
super.initState（）；
_iCounter=widget.iCounter；
}
无效增量计数（）{
if（widget.tfAllowChange）{
设置状态（（）=>this.\u iCounter++）；
widget.fnDataChanged（_iCounter）；
打印（“CounterWithStateMain:New count=$\u iCounter”）；
}
}
小部件构建（上下文）{
返回列（子项：[
文本（“计数器值=$\u i计数器”），
大小盒子(
身高：20.0，
),
升起的按钮(
onPressed:增加计数，
子项：文本（“点击添加”），
)
]);
}
}

这是我之前答案的更新，以更好地说明我想要实现的目标。我目前在我的代码中使用这个概念，使用复选框来存储它自己的值

这只是一个简单的例子（概念证明）来说明我想要实现的目标。我只是想让小部件存储它的值，并在我需要时将其提供给我（即更新数据）。另一种选择是由主程序存储值，但我认为这并不理想

以下内容似乎有效。它似乎比我高很多

import 'package:flutter/material.dart';

class CounterWithState {
  int _iCounter;
  CounterWithStateInternal _counterWithStateInternal;

  fnDataChanged(int iNewCounter) {
    _iCounter = iNewCounter;
    debugPrint("CounterWithState: New value = $_iCounter");
  }

  CounterWithStateInternal getCounterWidget() {
    return _counterWithStateInternal;
  }

  CounterWithState({@required iCounter, @required bool isAllowedChange}) {
    _iCounter = iCounter;
    _counterWithStateInternal = CounterWithStateInternal(
        GlobalKey(), this._iCounter, isAllowedChange, fnDataChanged);
  }
  get iCounter => _iCounter;
}

class CounterWithStateInternal extends StatefulWidget {
  final int iCounter;
  final bool tfAllowChange;
  final Function fnDataChanged;
  CounterWithStateInternal(
      Key key, this.iCounter, this.tfAllowChange, this.fnDataChanged)
      : super(key: key);
  @override
  CounterWithStateMain createState() => CounterWithStateMain();
}

class CounterWithStateMain extends State<CounterWithStateInternal> {
  int _iCounter = 0;

  @override
  initState() {
    super.initState();
    _iCounter = widget.iCounter;
  }

  void increaseCount() {
    if (widget.tfAllowChange) {
      setState(() => this._iCounter++);
      widget.fnDataChanged(_iCounter);
      print("CounterWithStateMain: New count = $_iCounter");
    }
  }

  Widget build(context) {
    return Column(children: <Widget>[
      Text("Value of counter = $_iCounter"),
      SizedBox(
        height: 20.0,
      ),
      RaisedButton(
        onPressed: increaseCount,
        child: Text('Tap To Add'),
      )
    ]);
  }
}

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

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  final String sTitle = 'Flutter Counter-With-State Demo';
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: sTitle,
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: sTitle),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);
  final String title;
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  CounterWithState _counterWithState;
  FloatingActionButton _fab;
  int _iCounterOriginal = 99;
  RaisedButton _raisedButton;
  SizedBox _sizedBox;
  final _scaffoldKey = GlobalKey<ScaffoldState>();

  @override
  void initState() {
    super.initState();
    _fab = FloatingActionButton(
      onPressed: _showSnackbar,
      tooltip: 'Press to show Counter',
      child: Icon(Icons.info),
    );
    _raisedButton = RaisedButton(
        child: const Text('Update'),
        color: Theme.of(context).accentColor,
        elevation: 4.0,
        splashColor: Colors.blueGrey,
        onPressed: () {
          _iCounterOriginal = _counterWithState.iCounter;
          _counterWithState = null;
          _getCounterWithState(context);
          setState(() {});
        });
    _sizedBox = SizedBox(height: _raisedButton.height);
  }

  fnCounterChanged(int iCounter) {
    setState(() {});
  }

  _showSnackbar() {
    _scaffoldKey.currentState.showSnackBar(SnackBar(
        backgroundColor: Colors.blue,
        content:
            Text("Current value of Counter is ${_counterWithState.iCounter}")));
  }

  @override
  Widget build(BuildContext context) {
    _counterWithState = _counterWithState != null
        ? _counterWithState
        : _getCounterWithState(context);
    return Scaffold(
      key: _scaffoldKey,
      appBar: AppBar(
        title: Text(widget.title),
        centerTitle: true,
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            _counterWithState.getCounterWidget(),
            _getUpdateButton(context),
          ],
        ),
      ),
      floatingActionButton: _fab,
    );
  }

  Widget _getUpdateButton(BuildContext context) {
    return _counterWithState == null ||
            _counterWithState.iCounter == _iCounterOriginal
        ? _sizedBox
        : _raisedButton;
  }

  CounterWithState _getCounterWithState(context) {
    if (_counterWithState == null)
      _counterWithState = CounterWithState(
          iCounter: _iCounterOriginal,
          isAllowedChange: true,
          fnNotifyChange: fnCounterChanged);
    return _counterWithState;
  }
}

import 'package:flutter/material.dart';

class CounterWithState {
  int _iCounter;
  final Function fnNotifyChange;
  CounterWithStateInternal _counterWithStateInternal;

  fnDataChanged(int iNewCounter) {
    _iCounter = iNewCounter;
    if (fnNotifyChange != null) fnNotifyChange(iNewCounter);
  }

  CounterWithStateInternal getCounterWidget() {
    return _counterWithStateInternal;
  }

  CounterWithState(
      {@required iCounter,
      @required bool isAllowedChange,
      this.fnNotifyChange}) {
    _iCounter = iCounter;
    _counterWithStateInternal = CounterWithStateInternal(
        GlobalKey(), this._iCounter, isAllowedChange, fnDataChanged);
  }
  get iCounter => _iCounter;
}

class CounterWithStateInternal extends StatefulWidget {
  final int iCounter;
  final bool tfAllowChange;
  final Function fnDataChanged;
  CounterWithStateInternal(
      Key key, this.iCounter, this.tfAllowChange, this.fnDataChanged)
      : super(key: key);
  @override
  CounterWithStateMain createState() => CounterWithStateMain();
}

class CounterWithStateMain extends State<CounterWithStateInternal> {
  int _iCounter;
  int _iOriginalCounter;

  @override
  initState() {
    super.initState();
    _iCounter = widget.iCounter;
    _iOriginalCounter = widget.iCounter;
  }

  void incrementCounter(int iValue) {
    if (widget.tfAllowChange) {
      setState(() => this._iCounter += iValue);
      widget.fnDataChanged(_iCounter);
    }
  }

  Widget build(context) {
    return Column(children: <Widget>[
      Text("Value of original counter = $_iOriginalCounter"),
      _getSizedBox(),
      Text("Value of counter = $_iCounter"),
      _getSizedBox(),
      RaisedButton(
        onPressed: (() => incrementCounter(1)),
        child: Text('Tap To Add'),
      ),
      _getSizedBox(),
      RaisedButton(
        onPressed: (() => incrementCounter(-1)),
        child: Text('Tap To Subtract'),
      ),
      _getSizedBox(),
    ]);
  }

  SizedBox _getSizedBox() {
    return SizedBox(height: 20.0);
  }
}