Flutter Radio Button在单击时不改变值/也不改变活动颜色

Question

我已经尝试在 Flutter 中遵循 Radio 类的教程，但是当我单击它时，按钮并没有改变颜色。我知道设备正在读取点击次数，因为每当单击按钮但按钮颜色没有改变时，我都会放置一个打印语句来显示。

我就是不知道问题出在哪里

int radioValue = -1;

void _handleRadioValueChanged (int value){
  setState(() {
    radioValue = value;
    print(radioValue);
  });
}

return new Scaffold(
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Radio<int>(
                activeColor: Colors.green,
                value: 0,
                groupValue: radioValue,
                onChanged: _handleRadioValueChanged),

        new Radio<int>(
            activeColor: Colors.green,
            value: 1,
            groupValue: radioValue,
            onChanged: _handleRadioValueChanged),

        new Radio <int>(
            activeColor: Colors.green,
            value: 2,
            groupValue: radioValue,
            onChanged: _handleRadioValueChanged),

    ),
  )
);

我希望按钮在按下时会发生变化，但它只是保持在值 =-1 的状态；

Answer 1

下面是代码：

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: HomePage(),
    );
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  int radioValue = -1;

  void _handleRadioValueChanged(int value) {
    setState(() {
      radioValue = value;
      print(radioValue);
    });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
        body: new Center(
      child: new Column(mainAxisAlignment: MainAxisAlignment.center, children: [
        new Radio(
            activeColor: Colors.green,
            value: 0,
            groupValue: radioValue,
            onChanged: _handleRadioValueChanged),
        new Radio<int>(
            activeColor: Colors.green,
            value: 1,
            groupValue: radioValue,
            onChanged: _handleRadioValueChanged),
        new Radio<int>(
            activeColor: Colors.green,
            value: 2,
            groupValue: radioValue,
            onChanged: _handleRadioValueChanged),
      ]),
    ));
  }
}

Desired Output