如何让flutter google地图中的标记随相机移动而不是随地图移动

dependencies:
  google_maps_flutter: ^2.0.9

import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';

class MapScreen extends StatefulWidget {
  @override
  _MapScreenState createState() => _MapScreenState();
}

class _MapScreenState extends State<MapScreen> {
  GoogleMapController? _mapController;
  Marker? _marker;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Google Map'),
      ),
      body: GoogleMap(
        onMapCreated: (controller) {
          _mapController = controller;
        },
        onCameraMove: (position) {
          if (_marker != null) {
            _updateMarkerPosition(position.target);
          }
        },
        initialCameraPosition: CameraPosition(
          target: LatLng(37.7749, -122.4194), // 初始地图位置
          zoom: 12.0,
        ),
        markers: Set<Marker>.of([_marker!]),
      ),
    );
  }

  void _updateMarkerPosition(LatLng position) {
    setState(() {
      _marker = _marker!.copyWith(
        positionParam: position,
      );
    });
  }

  @override
  void initState() {
    super.initState();
    _marker = Marker(
      markerId: MarkerId('marker_1'),
      position: LatLng(37.7749, -122.4194), // 初始标记位置
    );
  }
}