我正在尝试创建地图屏幕,但发现以下错误:
======== Exception caught by widgets library =======================================================
The following LateError was thrown building Consumer<MapViewModel>(dirty, dependencies: [_InheritedProviderScope<MapViewModel>]):
LateInitializationError: Field 'initialPosition' has not been initialized.
The relevant error-causing widget was:
Consumer<MapViewModel> file:///Users/mahmoudalharoon/Desktop/Air%20Forces/aireforces/lib/screens/BaseScreen.dart:44:14
When the exception was thrown, this was the stack:
#0 MapViewModel.initialPosition (package:airforces/screens/map/viewmodel/map_viewmodel.dart)
#1 MapScreen.build.<anonymous closure> (package:airforces/screens/map/view/map_screen.dart:19:27)
#2 Consumer.buildWithChild (package:provider/src/consumer.dart:180:19)
#3 SingleChildStatelessWidget.build (package:nested/nested.dart:259:41)
#4 StatelessElement.build (package:flutter/src/widgets/framework.dart:4648:28)
...
====================================================================================================
这是我拥有的以下ViewModel
:
import 'package:airforces/enums/ScreenState.dart';
import 'package:airforces/screens/BaseViewModel.dart';
import 'package:geocoding/geocoding.dart';
import 'package:geolocator/geolocator.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
class MapViewModel extends BaseViewModel {
late LatLng? initialPosition;
late LatLng lastMapPosition = initialPosition!;
void getUserLocation() async {
Position position = await Geolocator.getCurrentPosition(
desiredAccuracy: LocationAccuracy.high);
List<Placemark> placemarks = await placemarkFromCoordinates(
position.latitude, position.longitude);
initialPosition = LatLng(position.latitude, position.longitude);
print('${placemarks[0].name}');
setState(ViewState.Idle);
}
}
这是我拥有的以下地图屏幕:
import 'package:airforces/screens/BaseScreen.dart';
import 'package:airforces/screens/map/viewmodel/map_viewmodel.dart';
import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
class MapScreen extends StatelessWidget {
@override
Widget build(BuildContext context) {
return BaseScreen<MapViewModel>(
onFinish: (_) {
},
onModelReady: (mapViewModel) {
mapViewModel.getUserLocation();
},
builder: (context, mapViewModel, child){
return GoogleMap(
initialCameraPosition: CameraPosition(
target: mapViewModel.initialPosition!,
),
myLocationEnabled: true,
);
},
);
}
}
答案 0 :(得分:1)
出现此问题是因为 initialPosition
是 null
,直到 late
初始化发生,但在此处发生后期初始化之前它被转换为不可为空的类型:{{1 }}。
您可以通过以下两种方法之一解决此问题。
mapViewModel.initialPosition!
为 initialPosition
,则返回默认位置。null
target: mapViewModel.initialPosition ?? [defaultPosition];
之前显示加载小部件,然后显示 initialPosition
。这两种解决方案都需要一个次要的状态管理解决方案,以便在 GoogleMap
最终初始化时更新小部件。