flutter - 在颤动中使变量整洁

Question

我正在制作一个包含很多开关的页面，当单击第一个开关时，开关下方会出现一个文本字段。如果我使用大约 10 个开关，当然每个开关需要 10 个不同的变量。但是当我像这样结合它时。

断言失败：出现第 35 行标题 15 错误：'tristate || 价值！= null' 不正确

.

 `bool isSwitchedA, isSwitchedB, isSwitchedC, isSwitchedD, isSwitchedE, isSwitchedF = false;
  bool isSwitchedG, isSwitchedH, isSwitchedI, isSwitchedJ, isSwitchedK, isSwitchedL = false;
  bool isSwitchedM = false;`.

我做了一个特殊的小部件来调用开关，当然我也发送了一个开关变量，像这样_filterField(label = "Code", hintText = "enter code", swicths = isSwitchedA),

这是我的开关小部件

 Widget _filterField(String label, String hintText) {
return Column(
  children: <Widget>[
    Row(
      children: <Widget>[
        Switch(
          value: isSwitchedM,
          onChanged: (value) {
            _onChanged(true, value);
          },
          activeTrackColor: Colors.orangeAccent,
          activeColor: Colors.orange[900],
        ),
        Text(
          label,
          style: TextStyle(fontFamily: 'Ubuntu', fontSize: 14.0),
        ),
      ],
    ),
  ],
);

即使当我尝试使用 isSwitchedM 时，它也会出现，那么我该如何使用另一个 isSwitched 呢？

标签： flutterdart

Answer 1

您可以使用布尔列表来控制和传递开关索引

List<bool> isSwitchList = [false, false];

代码片段

Widget _filterField({String label, String hintText, int switchIndex}) {
    return Column(
      children: <Widget>[
        Row(
          children: <Widget>[
            Switch(
              value: isSwitchList[switchIndex],
              onChanged: (value) {
                print('${switchIndex}  ${isSwitchList[switchIndex]}');

                setState(() {
                  isSwitchList[switchIndex] = value;
                });

                print('${switchIndex}  ${isSwitchList[switchIndex]}');
              },
              activeTrackColor: Colors.orangeAccent,
              activeColor: Colors.orange[900],
            ),
            Text(
              label,
              style: TextStyle(fontFamily: 'Ubuntu', fontSize: 14.0),
            ),
          ],
        ),
      ],
    );
  }

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: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

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;
  List<bool> isSwitchList = [false, false];

  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>[
            _filterField(label: "Code 1", hintText:  "enter code 1", switchIndex: 0),
            _filterField(label: "Code 2", hintText:  "enter code 2", switchIndex: 1),
            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.
    );
  }

  void _onChangedCallback(bool ) {

  }

  Widget _filterField({String label, String hintText, int switchIndex}) {
    return Column(
      children: <Widget>[
        Row(
          children: <Widget>[
            Switch(
              value: isSwitchList[switchIndex],
              onChanged: (value) {
                print('${switchIndex}  ${isSwitchList[switchIndex]}');

                setState(() {
                  isSwitchList[switchIndex] = value;
                });

                print('${switchIndex}  ${isSwitchList[switchIndex]}');
              },
              activeTrackColor: Colors.orangeAccent,
              activeColor: Colors.orange[900],
            ),
            Text(
              label,
              style: TextStyle(fontFamily: 'Ubuntu', fontSize: 14.0),
            ),
          ],
        ),
      ],
    );
  }

}