谷歌地图上的当前位置（Flutter）

Question

I try to get current location my device and use it in initialCameraPosition,

The function is executed and I get the coordinates and set it in _currentPosition

After starting the screen i have an error:

LateError (LateInitializationError: Field 'currentPosition' has not been initialized.)

I think, map is created faster than the data is written to the variable, but i dont know how it fix.

Thanks fo help or advice how make code is correct

import 'package:flutter/material.dart';

import 'package:google_maps_flutter/google_maps_flutter.dart';

import 'package:geolocator/geolocator.dart';

class UserMapInfo extends StatefulWidget {
  const UserMapInfo({Key? key}) : super(key: key);

  @override
  State<UserMapInfo> createState() => _UserMapInfoState();
}

class _UserMapInfoState extends State<UserMapInfo> {
  late GoogleMapController mapController;

  late LatLng _currentPosition;

  @override
  void initState() {
    super.initState();
    getLocation();
  }

  getLocation() async {
    LocationPermission permission;
    permission = await Geolocator.requestPermission();

    Position position = await Geolocator.getCurrentPosition(
        desiredAccuracy: LocationAccuracy.high);
    double lat = position.latitude;
    double long = position.longitude;

    LatLng location = LatLng(lat, long);

    setState(() {
      _currentPosition = location;
    });
  }

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Map'),
      ),
      body: GoogleMap(
        onMapCreated: _onMapCreated,
        initialCameraPosition: CameraPosition(
          target: _currentPosition,
          zoom: 16.0,
        ),
      ),
    );
  }
}

Update

I try to use

LatLng? _currentPosition;

and add test coordinates

LatLng basePosition = LatLng(56.324293441187315, 38.13961947281509);

and add "null check"

my code

class _UserMapInfoState extends State<UserMapInfo> {
  
  late GoogleMapController mapController;

  // late LatLng currentPosition;

  LatLng? _currentPosition;

  LatLng basePosition = LatLng(56.324293441187315, 38.13961947281509);

  @override
  void initState() {
    super.initState();
    getLocation();
  }

  getLocation() async {
    LocationPermission permission;
    permission = await Geolocator.requestPermission();

    Position position = await Geolocator.getCurrentPosition(
        desiredAccuracy: LocationAccuracy.high);
    double lat = position.latitude;
    double long = position.longitude;

    LatLng location = LatLng(lat, long);

    setState(() {
      _currentPosition = location;
    });
  }

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Map'),
      ),
      body: GoogleMap(
        onMapCreated: _onMapCreated,
        initialCameraPosition: CameraPosition(
          target: _currentPosition ?? basePosition,
          zoom: 16.0,
        ),
      ),
    );
  }
}

And when my map is open, use LatLng basePosition ((( this is not what i need

I try other null check

initialCameraPosition: CameraPosition(
          target: _currentPosition!,
          zoom: 16.0,
        ),

ERROR again

_CastError (Null check operator used on a null value)

Thanks! Good solution!

And i`m add "null check" there

final code

import 'package:flutter/material.dart';

import 'package:google_maps_flutter/google_maps_flutter.dart';

import 'package:geolocator/geolocator.dart';

class UserMapInfo extends StatefulWidget {
  const UserMapInfo({Key? key}) : super(key: key);

  @override
  State<UserMapInfo> createState() => _UserMapInfoState();
}

class _UserMapInfoState extends State<UserMapInfo> {
  late GoogleMapController mapController;

  LatLng? _currentPosition;

  bool _isLoading = true;

  @override
  void initState() {
    super.initState();
    getLocation();
  }

  getLocation() async {
    LocationPermission permission;
    permission = await Geolocator.requestPermission();

    Position position = await Geolocator.getCurrentPosition(
        desiredAccuracy: LocationAccuracy.high);
    double lat = position.latitude;
    double long = position.longitude;

    LatLng location = LatLng(lat, long);

    setState(() {
      _currentPosition = location;
      _isLoading = false;
    });
  }

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Map'),
      ),
      body: _isLoading
          ? const Center(
              child: CircularProgressIndicator(),
            )
          : GoogleMap(
              onMapCreated: _onMapCreated,
              initialCameraPosition: CameraPosition(
                target: _currentPosition!,
                zoom: 16.0,
              ),
            ),
    );
  }
}

Answer 1

Try this:

class _UserMapInfoState extends State<UserMapInfo> {
  
  late GoogleMapController mapController;

  LatLng? _currentPosition;
  bool _isLoading = true;

  @override
  void initState() {
    super.initState();
    getLocation();
  }

  getLocation() async {
    LocationPermission permission;
    permission = await Geolocator.requestPermission();

    Position position = await Geolocator.getCurrentPosition(
        desiredAccuracy: LocationAccuracy.high);
    double lat = position.latitude;
    double long = position.longitude;

    LatLng location = LatLng(lat, long);

    setState(() {
      _currentPosition = location;
      _isLoading = false;
    });
  }

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Map'),
      ),
      body: _isLoading ? 
      Center(child:CircularProgressIndicator()) : 
      GoogleMap(
        onMapCreated: _onMapCreated,
        initialCameraPosition: CameraPosition(
          target: _currentPosition,
          zoom: 16.0,
        ),
      ),
    );
  }
}

Answer 2

This is happening because getLocation() is a async method and you have to wait for it to finish before creating your map widget with _currentPosition

Below code is a quick solution:

class MapPage extends StatefulWidget {
  const MapPage({Key? key}) : super(key: key);

  @override
  State<MapPage> createState() => _MapPageState();
}

class _MapPageState extends State<MapPage> {
  late GoogleMapController mapController;
  late Future _getCurrentLocationFuture;
  LatLng? _currentPosition;

  @override
  void initState() {
    _getCurrentLocationFuture = _getCurrentLocation();
    super.initState();
  }

  _getCurrentLocation() async {
    Position position;
    try {
      position = await Geolocator.getCurrentPosition(
          desiredAccuracy: LocationAccuracy.high,
          forceAndroidLocationManager: true,
          timeLimit: Duration(seconds: 15));
    } catch (e) {
      position = null;
      debugPrint(e);
    }

    if (position != null) {
      LatLng location = LatLng(position.latitude, position.longitude);
      _currentPosition = location;
    }

    return true;
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: FutureBuilder(
        future: _getCurrentLocationFuture,
        builder: (context, snapshot) {
          if (snapshot.hasData) {
            return GoogleMap(
              onMapCreated: _onMapCreated,
              initialCameraPosition: CameraPosition(
                target: _currentPosition ??
                    LatLng(56.324293441187315, 38.13961947281509),
                zoom: 16.0,
              ),
            );
          } else {
            return CircularProgressIndicator();
          }
        },
      ),
    );
  }

  void _onMapCreated(GoogleMapController controller) {
    mapController = controller;
  }
}

Also its best to check location permission and service before opening MapPage . or you can check it inside MapPage and then use animateCamera to move the map to current location