使用 geolocator 和 provider 以及 flutter_maps 获取位置

Question

我正在尝试使用地理定位器插件获取用户当前位置，并且我正在使用提供程序包来处理状态。但我收到“初始位置为空”错误消息。我使用的是 flutter_maps 包，而不是谷歌地图。

我尝试使用提供程序包寻找解决方案，但没有找到。

这是我的代码：

main.dart：

import 'package:flutter/material.dart';

import 'package:provider/provider.dart';

import './maps_module/map_states.dart';
import 'home_page.dart';


void main() {
  WidgetsFlutterBinding.ensureInitialized();
  return runApp(
    MultiProvider(
      providers: [
        ChangeNotifierProvider.value(value: AppState())
      ],
      child: MyApp(),
    )
  );
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: HomePage(),
    );
  }
}

home_page.dart：

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:latlong/latlong.dart';
import 'package:geolocator/geolocator.dart';

import './maps_module/map_states.dart';
import './maps_module/maps_screen.dart';


class HomePage extends StatelessWidget {

  @override
  Widget build(BuildContext context) {

    final appState = Provider.of<AppState>(context);

    return Scaffold(
      body: appState.initialPosition == null?
      Center(
        child: CircularProgressIndicator(),
      )
      :MapScreen(),
    );
  }
}

map_screen.dart：

import 'package:flutter/material.dart';

import 'package:provider/provider.dart';
import 'package:flutter_map/flutter_map.dart';
import 'package:latlong/latlong.dart';

import 'map_states.dart';


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

class _MapScreenState extends State<MapScreen> {

  @override
  Widget build(BuildContext context) {

    final appState = Provider.of<AppState>(context);

    return SafeArea(
      child: Scaffold(
        // appBar: AppBar(),
        body: FlutterMap(
          mapController: appState.mapController,
          options: MapOptions(
            center: LatLng(appState.initialPosition.latitude, appState.initialPosition.longitude),
            minZoom: 10.0
          ),
          layers: [
            TileLayerOptions(
              urlTemplate: "https://{s}.tile.openstreetmap.org/{z}/{x}/{y}.png",
              subdomains: ['a','b','c']
            ),
            MarkerLayerOptions(
              markers: [
                Marker(
                  width: 80.0,
                  height: 80.0,
                  point: appState.initialPosition,
                  builder: (context) =>
                  Container(
                    child: IconButton(
                      icon: Icon(Icons.location_on),
                      color: Colors.redAccent,
                      iconSize: 45.0,
                      onPressed: (){print("hey");}
                    ),
                  )
                )
              ]
            )
          ],
        ),
      )
    );
  }
}

地图状态：

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

import 'package:flutter_map/flutter_map.dart';
import 'package:geolocator/geolocator.dart';
import 'package:latlong/latlong.dart';


class AppState with ChangeNotifier {

  bool locationServiceActive = true;

  MapController _mapController;
  MapController get mapController => _mapController;

  static var _initialPosition;
  var _lastPosition = _initialPosition;
  LatLng get initialPosition => _initialPosition;
  LatLng get lastPosition => _lastPosition;

  AppState(){
    checkGPS();
    _getUserLocation();
  }


  checkGPS() async{
    bool conn = await Geolocator().isLocationServiceEnabled();
    if(conn == false){
      locationServiceActive = false;
    } else {
      locationServiceActive = true;
    }
    notifyListeners();
  }

  void _getUserLocation() async{
    Position position = await Geolocator().getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
    print("/////////////////////////////////////////////////////////////////////////////////position");
    print(position);

    _initialPosition = LatLng(position.latitude, position.longitude);
    notifyListeners();
  }
}

Answer 1

你的问题是你需要在你的类构造函数中awaitcheckgps()和_getUserLocation()问题是你不能从类的构造函数运行异步函数所以你需要做这样的事情.首先，您需要从 _getUserLocation() 中删除 void 或将其设为 Future<void> 然后添加。

//Add to your class 
initalization() async {
    await _checkGPS();
    await getUserLocation();
  }

//This in a widget will prove it works
 @override
  void initState() {
    AppState().initalization();
    print('Location ${AppState().initialPosition}');
    super.initState();
  }