SnackBar adalah widget untuk menampilkan pesan ringan di bagian bawah layar. Itu juga dapat berisi tindakan opsional. SnackBar biasanya digunakan dengan Scaffold dan penggunaannya ditunjukkan pada contoh di bawah ini.

edit pada file main.dart :

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Show Snackbar'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final GlobalKey<ScaffoldState> _scaffoldKey = new GlobalKey<ScaffoldState>();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      key: _scaffoldKey,
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: Row(
        mainAxisAlignment: MainAxisAlignment.center,
        children: <Widget>[
          Column(
            mainAxisAlignment: MainAxisAlignment.spaceEvenly,
            children: <Widget>[
              RaisedButton(
                  color: Colors.red,
                  child: Text('Snackbar that throws error'),
                  onPressed: () {
                    Scaffold.of(context).showSnackBar(SnackBar(
                          content: Text('It throws error'),
                          duration: Duration(seconds: 3),
                        ));
                  }),
              Builder(
                builder: (context) => RaisedButton(
                    color: Colors.green,
                    child: Text('Show Snackbar using context from Builder'),
                    onPressed: () {
                      Scaffold.of(context).showSnackBar(SnackBar(
                            content: Text('Context from Builder'),
                            duration: Duration(seconds: 3),
                          ));
                    }),
              ),
              SeparateWidget(),
              RaisedButton(
                  color: Colors.yellow,
                  child: Text('Show Snackbar using a GlobalKey'),
                  onPressed: () {
                    _scaffoldKey.currentState.showSnackBar(SnackBar(
                      content: Text('Assign a GlobalKey to the Scaffold'),
                      duration: Duration(seconds: 3),
                    ));
                  }),
            ],
          ),
        ],
      ),
      // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

class SeparateWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return RaisedButton(
        color: Colors.blueAccent,
        child: Text("Button moved to separate widget"),
        onPressed: () {
          Scaffold.of(context).showSnackBar(SnackBar(
                content: Text('Button moved to separate widget'),
                duration: Duration(seconds: 3),
              ));
        });
  }
}

outnya akan tampil seperti ini :