如何使用showModelBottomSheet创建DraggableScrollableSheet？

import 'package:flutter/material.dart';

final GlobalKey<ScaffoldState> _scaffoldKey = GlobalKey<ScaffoldState>();

void _showBottomSheet() {
  _scaffoldKey.currentState.showBottomSheet(
    (BuildContext context) {
      return DraggableScrollableSheet(
        expand: false,
        builder: (BuildContext context, ScrollController scrollController) {
          return Container(
            color: Colors.white,
            child: ListView.builder(
              controller: scrollController,
              itemCount: 50,
              itemBuilder: (BuildContext context, int index) {
                return ListTile(
                  title: Text('Item $index'),
                );
              },
            ),
          );
        },
      );
    },
  );
}

Scaffold(
  key: _scaffoldKey,
  appBar: AppBar(
    title: Text('My App'),
  ),
  body: Center(
    child: RaisedButton(
      child: Text('Open Bottom Sheet'),
      onPressed: _showBottomSheet,
    ),
  ),
);