Question

我在Flutter项目中实现了RadioButtons，并且那些RadioButtons的onChanged未被调用。我用TextField和CheckBox尝试了同样的方法，但两者都不起作用

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

class MyApp extends StatefulWidget {
  @override
  State<StatefulWidget> createState() {
    return MyAppState();
  }
}

class MyAppState extends State<MyApp> {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        title: "Different Widgets",
        debugShowCheckedModeBanner: false,
        home: _showRadioButton());
  }

  List<Widget> makeRadios() {
    int _selected = 0;

    void onChanged(int value) {
      setState(() {
        _selected = value;
      });
    }

    List<Widget> list = List<Widget>();

    for (int i = 0; i < 3; i++) {
      list.add(Row(
        children: <Widget>[
          Text("Radio"),
          Radio(
              value: i,
              groupValue: _selected,
              onChanged: (int value) {
                onChanged(value);
              })
        ],
      ));
    }

    for (int i = 0; i < 3; i++) {
      list.add(RadioListTile(
          value: i,
          groupValue: _selected,
          onChanged: (int value) {
            onChanged(value);
          },
        title: Text("title"),
      activeColor: Colors.red,
      secondary: Icon(Icons.access_alarm),
      subtitle: Text("Gender"),
      ));
    }

    return list;
  }

  Widget _showRadioButton() {
    return Scaffold(
      appBar: AppBar(
        title: Text("Hi"),
      ),
      body: Container(
        padding: EdgeInsets.all(10.0),
        child: Center(
          child: Column(
            children:
              makeRadios()

          ),
        ),
      ),
    );
  }

我不明白为什么未调用单选按钮的onChanged吗？ TextField和复选框的onChanged也不起作用。

Answer 1

以下解决方案对我有用

import 'package:flutter/material.dart';

void main() {
  runApp(new MaterialApp(
    home: new MyApp(),
  ));
}

class MyApp extends StatefulWidget {
  @override
  MyAppState createState() => new MyAppState();
}

class MyAppState extends State<MyApp> {

  int _selected = 0;

  void onChanged(int value) {
    setState((){
      _selected = value;
    });

    print('Value = $value');
  }

  List<Widget> makeRadios() {
    List<Widget> list = new List<Widget>();

    for(int i = 0; i < 3; i++) {
      list.add( new Row(
        children: <Widget>[
          new Text('Radio $i'),
          new Radio(value: i, groupValue: _selected, onChanged: (int value){onChanged(value);})
        ],
      ));
    }

    for(int i = 0; i < 3; i++) {
      list.add(new RadioListTile(
        value: i,
        title: new Text('Radio $i'),
        groupValue: _selected,
        onChanged: (int value){onChanged(value);},
        activeColor: Colors.red,
        secondary: new Icon(Icons.home),
        subtitle: new Text('Sub Title here'),
      ));
    }

    return list;
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Radio Demo'),
      ),
      body: new Container(
        padding: new EdgeInsets.all(32.0),
        child: new Center(
          child:  new Column(
            children: makeRadios(),
          ),
        ),
      ),
    );
  }
}

我仍然感到困惑，为什么问题中提到的解决方案不起作用

Flutter onChanged不会被任何小部件调用

1 个答案: