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android - Flutter "The getter 'latitude' was called on null" when using GeoLocator

问题描述

I am trying to get the position of a user. I am using GeoLocator and google_maps_flutter dependencies to do this.

When building I get an error for a split second when switching from the login screen to the google map screen. The error I am seeing in the console is...

The following NoSuchMethodError was thrown building googleMaps(dirty, state: MapAppState#bc232):
The getter 'latitude' was called on null.
Receiver: null
Tried calling: latitude

My code is..

class googleMaps extends StatefulWidget {
  @override
  MapAppState createState() => MapAppState();
}

class MapAppState extends State<googleMaps> {
  GoogleMapController mapController;
  Position position;
  static LatLng _initialPosition;
  static LatLng _lastMapPosition = _initialPosition;

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

  void getLocation() async {
    position = await Geolocator.getCurrentPosition(desiredAccuracy: LocationAccuracy.high);
    setState(() {
      _initialPosition = LatLng(position.latitude, position.longitude);
    });
  }

  @override
  Widget build(BuildContext context) {
    getLocation();
    return MaterialApp(
      home: Scaffold(
        body: GoogleMap(
          onMapCreated: _onMapCreated,
          initialCameraPosition: CameraPosition(
            target: LatLng(position.latitude, position.longitude),
            zoom: 11.0,
          ),
          gestureRecognizers: <Factory<OneSequenceGestureRecognizer>>[
            new Factory<OneSequenceGestureRecognizer>(
              () => new EagerGestureRecognizer(),
            ),
          ].toSet(),
          cameraTargetBounds: CameraTargetBounds.unbounded,
          minMaxZoomPreference: MinMaxZoomPreference.unbounded,
          rotateGesturesEnabled: true,
          scrollGesturesEnabled: true,
          zoomGesturesEnabled: true,
          tiltGesturesEnabled: true,
          myLocationButtonEnabled: true,
          myLocationEnabled: true,
        ),
      ),
    );
  }
}

I seen someone suggested using FutureBuilder but I do not believe I would like to take this route for fixing the error. Could someone point me in the right direction for fixing this error?

Thanks in advance!

标签： androidflutterdart

解决方案

当您调用 getLocation() 时，它不会在阻塞庄园中被调用。因此，当创建 GoogleMap 小部件时，颤动事件循环尚未收到位置。对此的快速解决方法是在 getLocation() 之前调用 await。不幸的是，这会使屏幕加载时间变慢。一个更持久的修复方法是将 _initalPosition 设置为预定的 LatLng 或将用户的最后位置保存在 sharedPreferences 中并将其设置为该值以开始。这样，UI 仍然可以快速加载，并且 setState() 调用可以稍后更新 UI。

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