Flutter BottomSheet底部弹窗效果

import 'package:flutter/material.dart';
import 'dart:async';
class BottomSheetDemo extendsStatefulWidget {
  @override
  _BottomSheetDemoState createState() =>_BottomSheetDemoState();
}
class _BottomSheetDemoState extends State<BottomSheetDemo>{
  final _bottomSheetScaffoldKey = GlobalKey<ScaffoldState>();
  _openBottomSheet() {
    _bottomSheetScaffoldKey
      .currentState
      .showBottomSheet((BuildContext context) {
        returnBottomAppBar(
          child: Container(
            height: 90.0,
             double.infinity,
            padding: EdgeInsets.all(16.0),
            child: Row(
              children: <Widget>[
                Icon(Icons.pause_circle_outline),
                SizedBox( 16.0,),
                Text('01:30 / 03:30'),
                Expanded(
                  child: Text('从头再来-刘欢', textAlign: TextAlign.right,),
                ),
              ],
            ),
          ),
        );
      });
  }
  Future _openModalBottomSheet() async {
    final option =await showModalBottomSheet(
      context: context,
      builder: (BuildContext context) {
        returnContainer(
          height: 200.0,
          child: Column(
            children: <Widget>[
              ListTile(
                title: Text('拍照',textAlign: TextAlign.center),
                onTap: () {
                  Navigator.pop(context, '拍照');
                },
              ),
              ListTile(
                title: Text('从相册选择',textAlign: TextAlign.center),
                onTap: () {
                  Navigator.pop(context, '从相册选择');
                },
              ),
              ListTile(
                title: Text('取消',textAlign: TextAlign.center),
                onTap: () {
                  Navigator.pop(context, '取消');
                },
              ),
            ],
          ),
        );
      }
    );
    print(option);
  }
  @override
  Widget build(BuildContext context) {
    returnScaffold(
      key: _bottomSheetScaffoldKey,
      appBar: AppBar(
        title: Text('BottomSheetDemo'),
        elevation: 0.0,
      ),
      body: Container(
        padding: EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Row(
              mainAxisAlignment: MainAxisAlignment.center,
              children: <Widget>[
                FlatButton(
                  child: Text('Open BottomSheet'),
                  onPressed: _openBottomSheet,
                ),
                FlatButton(
                  child: Text('Modal BottomSheet'),
                  onPressed: _openModalBottomSheet,
                ),
              ]
            ),
          ],
        ),
      ),
    );
  }
}