Flutter Google 地图初始位置为空？

Question

目的是加载页面并根据设备的 GPS 在 Google 地图中显示当前位置。

下面的代码有什么问题？看来它不想等待位置并返回“空值检查运算符使用于空值”。

我无法找到答案，希望得到一些帮助。

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

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

  @override
  State<FindSomeonePage> createState() => _FindSomeonePageState();
}

class _FindSomeonePageState extends State<FindSomeonePage> {
  LatLng? _initialLocation;
  late GoogleMapController mapController;

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

  _setInitialLocation() async {
    LocationData? currentLocation = await getCurrentLocation();
    if (currentLocation != null) {
      setState(() {
        _initialLocation =
            LatLng(currentLocation.latitude!, currentLocation.longitude!);
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        body: Stack(
          children: [
            GoogleMap(
              //LatLng(-15.4630239974464, 28.363397732282127)
              initialCameraPosition: CameraPosition(
                target: _initialLocation!,
                zoom: 15.0,
              ),
              onMapCreated: (controller) {
                mapController = controller;
              },
            ),
          ],
        ),
      ),
    );
  }
}

Future<LocationData?> getCurrentLocation() async {
  Location location = new Location();

  bool _serviceEnabled;
  PermissionStatus _permissionGranted;

  _serviceEnabled = await location.serviceEnabled();
  if (!_serviceEnabled) {
    _serviceEnabled = await location.requestService();
    if (!_serviceEnabled) {
      return null;
    }
  }

  _permissionGranted = await location.hasPermission();
  if (_permissionGranted == PermissionStatus.denied) {
    _permissionGranted = await location.requestPermission();
    if (_permissionGranted != PermissionStatus.granted) {
      return null;
    }
  }

  return await location.getLocation();
}

Answer 1

您收到该错误是因为

_initialLocation

最初为空，并且您在小部件的主体中使用它，而没有检查该值是否为空，也没有等待

getCurrentLocation()

的结果。

要解决此问题，您需要在获取

currentLocation

时向您的小部件显示加载微调器。

首先，初始化一个

_isLoading

变量：

bool _isLoading = false;

那么你的

_setInitialLocation

应该是：

_setInitialLocation() async {
_isLoading = true;
    LocationData? currentLocation = await getCurrentLocation();
    if (currentLocation != null) {
       _initialLocation =
            LatLng(currentLocation.latitude!, currentLocation.longitude!);
    }
    ///this rebuilds your widget whether or not the fetch location is successful
///It is then your responsibility to show error to your widget when error occur.
      setState(() {
_isLoading = false;
      });
  }

你的小部件的主体应该是：

  @override
  Widget build(BuildContext context) {
    return SafeArea(
      child: Scaffold(
        body: _isLoading ? CircularProgressIndicator() : Stack(
          children: [

if(_initialLocation != null)...[
 GoogleMap(
              //LatLng(-15.4630239974464, 28.363397732282127)
              initialCameraPosition: CameraPosition(
                target: _initialLocation!,
                zoom: 15.0,
              ),
              onMapCreated: (controller) {
                mapController = controller;
              },
            ),
]
           
          ],
        ),
      ),
    );
  }
}