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

// Copyright 2015 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';

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

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

class _PersistentBottomSheetDemoState extends State<PersistentBottomSheetDemo> {
  final GlobalKey<ScaffoldState> _scaffoldKey = new 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 new Container(
        decoration: new BoxDecoration(
          border: new Border(top: new BorderSide(color: themeData.disabledColor))
        ),
        child: new Padding(
          padding: const EdgeInsets.all(32.0),
          child: new Text('This is a Material persistent bottom sheet. Drag downwards to dismiss it.',
            textAlign: TextAlign.center,
            style: new TextStyle(
              color: themeData.accentColor,
              fontSize: 24.0
            )
          )
        )
      );
    })
    .closed.whenComplete(() {
      if (mounted) {
        setState(() { // re-enable the button
          _showBottomSheetCallback = _showBottomSheet;
        });
      }
    });
  }

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

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      key: _scaffoldKey,
      appBar: new AppBar(title: new Text('Persistent bottom sheet')),
      floatingActionButton: new FloatingActionButton(
        onPressed: _showMessage,
        backgroundColor: Colors.redAccent[200],
        child: new Icon(Icons.add)
      ),
      body: new Center(
        child: new RaisedButton(
          onPressed: _showBottomSheetCallback,
          child: new Text('SHOW BOTTOM SHEET')
        )
      )
    );
  }
}