samples/web/gallery/lib/demo/material/persistent_bottom_sheet_demo.dart

// Copyright 2018 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_web/material.dart';

import '../../gallery/demo.dart';

class PersistentBottomSheetDemo extends StatefulWidget {
  static const String routeName = '/material/persistent-bottom-sheet';

  @override
  _PersistentBottomSheetDemoState createState() =>
      _PersistentBottomSheetDemoState();
}

class _PersistentBottomSheetDemoState extends State<PersistentBottomSheetDemo> {
  final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

  VoidCallback _showBottomSheetCallback;

  @override
  void initState() {
    super.initState();
    _showBottomSheetCallback = _showBottomSheet;
  }

  void _showBottomSheet() {
    setState(() {
      // disable the button
      _showBottomSheetCallback = null;
    });
    _scaffoldKey.currentState
        .showBottomSheet<Null>((BuildContext context) {
          final ThemeData themeData = Theme.of(context);
          return Container(
            decoration: BoxDecoration(
                border:
                    Border(top: BorderSide(color: themeData.disabledColor))),
            child: Padding(
              padding: const EdgeInsets.all(32.0),
              child: Text(
                'This is a Material persistent bottom sheet. Drag downwards to dismiss it.',
                textAlign: TextAlign.center,
                style: TextStyle(color: themeData.accentColor, fontSize: 24.0),
              ),
            ),
          );
        })
        .closed
        .whenComplete(() {
          if (mounted) {
            setState(() {
              // re-enable the button
              _showBottomSheetCallback = _showBottomSheet;
            });
          }
        });
  }

  void _showMessage() {
    showDialog<void>(
      context: context,
      builder: (BuildContext context) {
        return AlertDialog(
          content: const Text('You tapped the floating action button.'),
          actions: <Widget>[
            FlatButton(
                onPressed: () {
                  Navigator.pop(context);
                },
                child: const Text('OK'))
          ],
        );
      },
    );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        key: _scaffoldKey,
        appBar: AppBar(
          title: const Text('Persistent bottom sheet'),
          actions: <Widget>[
            MaterialDemoDocumentationButton(
                PersistentBottomSheetDemo.routeName),
          ],
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: _showMessage,
          backgroundColor: Colors.redAccent,
          child: const Icon(
            Icons.add,
            semanticLabel: 'Add',
          ),
        ),
        body: Center(
            child: RaisedButton(
                onPressed: _showBottomSheetCallback,
                child: const Text('SHOW BOTTOM SHEET'))));
  }
}