Flutter-SnackBar（操作提示栏）

class SnackBarDemo extends StatefulWidget {
  @override
  _SnackBarDemoState createState() => _SnackBarDemoState();
}

class _SnackBarDemoState extends State<SnackBarDemo> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('SnackBarDemo'),
      ),
      body: Container(
        padding: EdgeInsets.all(16),
        child: Center(
          child: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              SnackButton(),
            ],
          ),
        ),
      ),
    );
  }
}

class SnackButton extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return FlatButton(
      child: Text('Open SnackBar'),
      onPressed: (){
        Scaffold.of(context).showSnackBar(
          SnackBar(
            content: Text('Processing...'),
            action: SnackBarAction(
              label: 'OK',
              onPressed: (){},
            ),
          )
        );
      },
    );
  }
}