class SwitchDemo extends StatefulWidget {
  @override
  _SwitchDemoState createState() => _SwitchDemoState();
}

class _SwitchDemoState extends State<SwitchDemo> {
  bool _switchItemA = false;
  
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: Text('Switch'), elevation: 0.0,),
      body: Container(
        padding: EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            SwitchListTile( // 帶標(biāo)簽與圖標(biāo)的開(kāi)關(guān)
              value: _switchItemA,
              onChanged: (value) {
                setState(() {
                  _switchItemA = value;
                });
              },
              title: Text('開(kāi)關(guān)'),
              subtitle: Text('這是一個(gè)開(kāi)關(guān)'),
              secondary: Icon(_switchItemA ? Icons.visibility : Icons.visibility_off),
              selected: _switchItemA,
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                Text(_switchItemA ? '??' : '??', style: TextStyle(fontSize: 32.0),),
                Switch( // 開(kāi)關(guān)
                  value: _switchItemA,
                  onChanged: (value) {
                  setState(() {
                    _switchItemA = value;
                  });
                  }
                ),
              ],
            )
          ],
        ),
      ),
    );
  }
}