如何使用 Google Maps For Flutter 将初始相机位置设置为当前设备的纬度和经度

Question

我正在为我的应用程序使用 google maps flutter 插件。我希望初始相机位置目标（LatLng）与当前设备的纬度和经度完全相等，以便相机在启动时显示用户当前所在的位置。但是，我在尝试执行此操作时遇到了问题。我曾尝试使用 Location 和 Geolocator 包，但没有关于如何做我想要实现的目标的明确示例。

当我尝试使用currentLocation.latitude和currentLocation.longitude位置包作为相机目标中 Latlng 的值时，我遇到了以下错误。

“初始化器只能访问静态成员”

坦率地说，我不知道在这种情况下这意味着什么。我已经阅读了一些示例，但没有一个清楚地实现我真正想要实现的目标

import 'package:flutter/cupertino.dart';
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:location/location.dart';


class Map extends StatefulWidget {
  @override
  State<Map> createState() => MapState();
}

class MapState extends State<Map> {
  Completer<GoogleMapController> _controller = Completer();
  var currentLocation = LocationData;

  var location = new Location();

 Future _getLocation() async {
    try {
      location.onLocationChanged().listen((LocationData currentLocation) {
        print('Latitude:${currentLocation.latitude}');
        print('Longitude:${currentLocation.longitude}');
        return LatLng(currentLocation.latitude, currentLocation.longitude);
      });
    } catch (e) {
     print('ERROR:$e');
      currentLocation = null;
    }

  }
  static final CameraPosition _currentPosition = CameraPosition(
    target: LatLng(currentLocation.latitude  ,  currentLocation.longitude),
    zoom: 14.4746,
  );

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


  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      body: GoogleMap(
        mapType: MapType.normal,
        initialCameraPosition: _currentPosition,
        zoomGesturesEnabled: true,
        myLocationButtonEnabled: true,
        rotateGesturesEnabled: true,
        tiltGesturesEnabled: true,
        onMapCreated: (GoogleMapController controller) {
          _controller.complete(controller);
        },
      ),

    );
  }


}

那是我的代码片段在 _currentPosition 最终产生错误，它表示相机位置使用定位器包将其等同于当前设备的纬度和经度，但 Flutter 正在抱怨。我不知道如何正确地做到这一点。我希望 latlng 目标是设备的 latlng

Answer 1

在获取用户当前位置的同时显示地图小部件时出现错误的问题是，获取用户的实际当前位置是一个异步操作，因此在整个过程中初始位置将为空，因此我们创建了一个运行的条件等待异步操作完成然后显示地图，然后该值将为非空。我重构了代码并改用了 geolocator 包

import 'package:flutter/cupertino.dart';
import 'dart:async';
import 'package:flutter/material.dart';
import 'package:geolocator/geolocator.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';

class Map extends StatefulWidget {
  @override
  _MapState createState() => _MapState();
}

class _MapState extends State<Map> {
  Completer<GoogleMapController> controller1;

  //static LatLng _center = LatLng(-15.4630239974464, 28.363397732282127);
  static LatLng _initialPosition;
  final Set<Marker> _markers = {};
  static  LatLng _lastMapPosition = _initialPosition;

  @override
  void initState() {
    super.initState();
    _getUserLocation();
  }
  void _getUserLocation() async {
    Position position = await Geolocator().getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
    List<Placemark> placemark = await Geolocator().placemarkFromCoordinates(position.latitude, position.longitude);
    setState(() {
      _initialPosition = LatLng(position.latitude, position.longitude);
      print('${placemark[0].name}');
    });
  }


  _onMapCreated(GoogleMapController controller) {
    setState(() {
      controller1.complete(controller);
    });
  }

  MapType _currentMapType = MapType.normal;

  void _onMapTypeButtonPressed() {
    setState(() {
      _currentMapType = _currentMapType == MapType.normal
          ? MapType.satellite
          : MapType.normal;
    });
  }

  _onCameraMove(CameraPosition position) {
    _lastMapPosition = position.target;
  }

  _onAddMarkerButtonPressed() {
    setState(() {
      _markers.add(
          Marker(
              markerId: MarkerId(_lastMapPosition.toString()),
              position: _lastMapPosition,
              infoWindow: InfoWindow(
                  title: "Pizza Parlour",
                  snippet: "This is a snippet",
                  onTap: (){
                  }
              ),
              onTap: (){
              },

              icon: BitmapDescriptor.defaultMarker));
    });
  }
  Widget mapButton(Function function, Icon icon, Color color) {
    return RawMaterialButton(
      onPressed: function,
      child: icon,
      shape: new CircleBorder(),
      elevation: 2.0,
      fillColor: color,
      padding: const EdgeInsets.all(7.0),
    );
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: _initialPosition == null ? Container(child: Center(child:Text('loading map..', style: TextStyle(fontFamily: 'Avenir-Medium', color: Colors.grey[400]),),),) : Container(
        child: Stack(children: <Widget>[
          GoogleMap(
            markers: _markers,

            mapType: _currentMapType,
            initialCameraPosition: CameraPosition(
              target: _initialPosition,
              zoom: 14.4746,
            ),
            onMapCreated: _onMapCreated,
            zoomGesturesEnabled: true,
            onCameraMove: _onCameraMove,
            myLocationEnabled: true,
            compassEnabled: true,
            myLocationButtonEnabled: false,

          ),
          Align(
            alignment: Alignment.topRight,
            child: Container(
                margin: EdgeInsets.fromLTRB(0.0, 50.0, 0.0, 0.0),
                child: Column(
                  children: <Widget>[
                    mapButton(_onAddMarkerButtonPressed,
                        Icon(
                            Icons.add_location
                        ), Colors.blue),
                    mapButton(
                        _onMapTypeButtonPressed,
                        Icon(
                          IconData(0xf473,
                              fontFamily: CupertinoIcons.iconFont,
                              fontPackage: CupertinoIcons.iconFontPackage),
                        ),
                        Colors.green),
                  ],
                )),
          )
        ]),
      ),
    );
  }
}

Answer 2

您提到的错误意味着您正在尝试访问初始化程序内的非静态变量，这就是您的情况currentLocation。

由于类的每个实例的值currentLocation都不同MapState，因此您会收到上述错误。

删除static和final关键字并尝试在函数_currentPosition内设置变量，initState如下所示 -

class MapState extends State<Map> {
  Completer<GoogleMapController> _controller = Completer();
  var currentLocation = LocationData;

  var location = new Location();
  CameraPosition _currentPosition;

  Future _getLocation() async {
    try {
      location.onLocationChanged().listen((LocationData currentLocation) {
        print('Latitude:${currentLocation.latitude}');
        print('Longitude:${currentLocation.longitude}');
        return LatLng(currentLocation.latitude, currentLocation.longitude);
      });
    } catch (e) {
     print('ERROR:$e');
      currentLocation = null;
    }

  }

  @override
  void initState() {
    _getLocation();
    currentPosition = CameraPosition(
      target: LatLng(currentLocation.latitude  ,  currentLocation.longitude),
      zoom: 14.4746,
    );
    super.initState();
  }

  //Rest of the code remains same
}