BottomSheetDemo.dart

import 'package:flutter/material.dart';

class BottomSheetDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new BottomSheet(),
    );
  }
}

class BottomSheet extends StatefulWidget {
  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

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

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

  void _showBottomSheet() {
    setState(() {
      _showPersBottomSheetCallBack = null;
    });

    _scaffoldKey.currentState
        .showBottomSheet((context) {
      return new Container(
        height: 200.0,
        color: Colors.greenAccent,
        child: new Center(
          child: new Text("Hi BottomSheet"),
        ),
      );
    })
        .closed
        .whenComplete(() {
      if (mounted) {
        setState(() {
          _showPersBottomSheetCallBack = _showBottomSheet;
        });
      }
    });
  }

  void _showModalSheet() {
    showModalBottomSheet(
        context: context,
        builder: (builder) {
          return new Container(
            height: 500.0,
            color: Colors.greenAccent,
            child: new Center(
              child: new Text("Hi ModalSheet"),
            ),
          );
        });
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      key: _scaffoldKey,
      appBar: new AppBar(
        title: new Text("Flutter BottomSheet"),
      ),
      body: new Padding(
        padding: const EdgeInsets.all(20.0),
        child: new Center(
            child: new Column(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                new RaisedButton(
                  onPressed: _showPersBottomSheetCallBack,
                  child: new Text("Persistent"),
                ),
                new Padding(
                  padding: const EdgeInsets.only(top: 10.0),
                ),
                new RaisedButton(
                  onPressed: _showModalSheet,
                  child: new Text("Modal"),
                ),
              ],
            )),
      ),
    );
  }
}