flutter/examples/flutter_gallery/lib/demo/snack_bar_demo.dart

// Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

const String _text1 =
  "Snackbars provide lightweight feedback about an operation by "
  "showing a brief message at the bottom of the screen. Snackbars "
  "can contain an action.";

const String _text2 =
  "Snackbars should contain a single line of text directly related "
  "to the operation performed. They cannot contain icons.";

const String _text3 =
  "By default snackbars automatically disappear after a few seconds ";

class SnackBarDemo extends StatefulWidget {
  SnackBarDemo({ Key key }) : super(key: key);

  static const String routeName = '/snack-bar';

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

class _SnackBarDemoState extends State<SnackBarDemo> {
  int _snackBarIndex = 1;

  Widget buildBody(BuildContext context) {
    return new ListView(
      padding: const EdgeInsets.all(24.0),
      children: <Widget>[
        new Text(_text1),
        new Text(_text2),
        new Center(
          child: new RaisedButton(
            child: new Text('SHOW A SNACKBAR'),
            onPressed: () {
              final int thisSnackBarIndex = _snackBarIndex++;
              Scaffold.of(context).showSnackBar(new SnackBar(
                content: new Text('This is snackbar #$thisSnackBarIndex.'),
                action: new SnackBarAction(
                  label: 'ACTION',
                  onPressed: () {
                    Scaffold.of(context).showSnackBar(new SnackBar(
                      content: new Text('You pressed snackbar $thisSnackBarIndex\'s action.')
                    ));
                  }
                )
              ));
            }
          )
        ),
        new Text(_text3),
      ]
      .map((Widget child) {
        return new Container(
          margin: const EdgeInsets.symmetric(vertical: 12.0),
          child: child
        );
      })
      .toList()
    );
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text('Snackbar')
      ),
      body: new Builder(
        // Create an inner BuildContext so that the snackBar onPressed methods
        // can refer to the Scaffold with Scaffold.of().
        builder: buildBody
      )
    );
  }
}