如何在flutter中点击google地图标记后添加底页？

import 'package:google_maps_flutter/google_maps_flutter.dart';

class MapPage extends StatefulWidget {
  @override
  _MapPageState createState() => _MapPageState();
}

class _MapPageState extends State<MapPage> {
  GoogleMapController mapController;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Google Map'),
      ),
      body: GoogleMap(
        onMapCreated: (controller) {
          setState(() {
            mapController = controller;
          });
        },
        // 设置地图初始位置
        initialCameraPosition: CameraPosition(
          target: LatLng(37.42796133580664, -122.085749655962),
          zoom: 14.0,
        ),
        // 添加标记
        markers: _createMarkers(),
      ),
    );
  }

  Set<Marker> _createMarkers() {
    return <Marker>[
      Marker(
        markerId: MarkerId('1'),
        position: LatLng(37.42796133580664, -122.085749655962),
        onTap: () {
          // 在这里添加底页
          _showBottomSheet();
        },
      ),
    ].toSet();
  }

  void _showBottomSheet() {
    showModalBottomSheet(
      context: context,
      builder: (BuildContext context) {
        return Container(
          height: 200,
          child: Center(
            child: Text('底页内容'),
          ),
        );
      },
    );
  }
}