final snackBar = SnackBar( content: Text('Yay! A SnackBar!'), action: SnackBarAction( label: 'Undo', onPressed: () { // Some code to undo the change. }, ),
); // Find the Scaffold in the widget tree and use // it to show a SnackBar. Scaffold.of(context).showSnackBar(snackBar);

class MyApp extends StatelessWidget { @override Widget build(BuildContext context) { return new MaterialApp( title: 'Flutter', theme: new ThemeData( primarySwatch: Colors.blue, ), home: new MyHomePage(), ); }
}
class MyHomePage extends StatefulWidget { MyHomePage({Key key}) : super(key: key); @override _MyHomePageState createState() => new _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> { final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>(); @override void initState() { super.initState(); showInSnackBar("Some text"); } @override Widget build(BuildContext context) { return new Padding( key: _scaffoldKey, padding: const EdgeInsets.all(16.0), child: new Text("Simple Text") ); } void showInSnackBar(String value) { _scaffoldKey.currentState.showSnackBar(new SnackBar( content: new Text(value) )); }
}