flutter笔记（九）-----单选框Radio、RadioL

flutter笔记汇总

之前学习了复选框和开关，还有个单选框，这里看一下。

Radio

还是先看constructor

Radio<T>({
  Key key,
  @required T value,
  @required T groupValue,
  @required ValueChanged<T> onChanged,
  Color activeColor,
  MaterialTapTargetSize materialTapTargetSize
})

这个Widget的constructor很简单，这几个属性前边都介绍过，怎么用看demo。

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 new MaterialApp(
      home: Scaffold(
        body: RadioDemo()
      )
    );
  }
}

enum SingingCharacter { lafayette, jefferson }

class RadioDemo extends StatefulWidget {
  @override
  _RadioDemoState createState() => new _RadioDemoState();
}

class _RadioDemoState extends State<RadioDemo> {
  SingingCharacter _character = SingingCharacter.lafayette;

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: EdgeInsets.only(top: 20.0),
      child: Column(
        children: <Widget>[
          Radio(
            value: SingingCharacter.lafayette,
            groupValue: _character,
            activeColor: Colors.red,
            onChanged: (SingingCharacter value) {
              print(value);
              setState(() {
                _character = value;
              });
            },
          ),
          Radio(
            value: SingingCharacter.jefferson,
            groupValue: _character,
            onChanged: (SingingCharacter value) {
              print(value);
              setState(() {
                _character = value;
              });
            },
          )
        ]
      )
    );
  }
}

这里有点陌生的东西，接下来看一下。

enum

枚举类型。
官方文档挺详细的http://dart.goodev.org/guides/language/language-tour
这里就不详细说了

Column

这里简单介绍一下，后边再详细说，这个Widget可以简单的理解成列表类似于html里边的ul，子节点是children一组Widget。

T

看constructor的时候应该就发现了，多了个<T>，这个是泛型，<>里边是数据类型，例如想定义一个List里边只能放String,可以这样写

var str = new List<String>();

这里T是备用类型，实际上就是一个占位符。

RadioListTile

const RadioListTile<T>({
  Key key,
  @required T value,
  @required T groupValue,
  @required ValueChanged<T> onChanged,
  Color activeColor,
  Widget title,
  Widget subtitle,
  bool isThreeLine: false,
  bool dense,
  Widget secondary,
  bool selected: false,
  ListTitleControlAffinity controlAffinity: ListTileControlAffinity.platform
})

demo

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 new MaterialApp(
      home: Scaffold(
        body: RadioDemo()
      )
    );
  }
}

enum SingingCharacter { lafayette, jefferson }

class RadioDemo extends StatefulWidget {
  @override
  _RadioDemoState createState() => new _RadioDemoState();
}

class _RadioDemoState extends State<RadioDemo> {
  SingingCharacter _character = SingingCharacter.lafayette;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Column(
        children: <Widget>[
          RadioListTile<SingingCharacter>(
            value: SingingCharacter.lafayette,
            title: Text('lafayette'),
            groupValue: _character,
            activeColor: Colors.red,
            onChanged: (SingingCharacter value) {
              print(value);
              setState(() {
                _character = value;
              });
            },
          ),
          RadioListTile<SingingCharacter>(
            value: SingingCharacter.jefferson,
            title: Text('jefferson'),
            groupValue: _character,
            onChanged: (SingingCharacter value) {
              print(value);
              setState(() {
                _character = value;
              });
            },
          )
        ]
      )
    );
  }
}

和单独的Radio相比基本上没啥区别。
相对于Radio多出来的属性看这里：flutter笔记（七）-----复选框CheckBox、CheckboxListTile
CheckboxList里边已经详细说过了。