如何解决颤振中的"Failed assertion: line 22 pos 16: 'target != null' : is not true"

Question

我在我的扑动项目中实现谷歌地图，我得到这个错误失败的断言:第22行pos 16: 'target != null':不为真在我的移动设备上出现2秒的红色错误屏幕，然后地图就实现了。

如何解决?

下面是代码:

body: GoogleMap(
polylines: _polyLines,
markers: _markers,
mapType: MapType.normal,
initialCameraPosition: CameraPosition(
target: latLng,
zoom: 14,
),
onCameraMove: onCameraMove,
onMapCreated: (GoogleMapController controller) {
_controller.complete(controller);
},
myLocationEnabled: true,
),

Answer 1

先回答

所以我在这里做的是，首先我使用geolocator: ^6.1.13插件获得当前位置并简单地将其保存到一个变量中，直到获得当前位置显示空容器然后将当前位置传递给谷歌地图中的target值

class SelectionScreen extends StatefulWidget {
@override
State<StatefulWidget> createState() {
// TODO: implement createState
return _selectionScreen();
}
}
class _selectionScreen extends State<SelectionScreen> {
@override
initState() {
loading = false;
getCurrentLocation();
super.initState();
}
bool loading;
var start_currentPostion;
getCurrentLocation() async {
Position position = await Geolocator.getCurrentPosition(
desiredAccuracy: LocationAccuracy.high);
setState(() {
double latitude = position.latitude;
double longitude = position.longitude;
start_currentPostion = LatLng(latitude, longitude);
loading = true;
});
}
@override
Widget build(BuildContext context) {
// TODO: implement build
return Scaffold(
body: loading ? GoogleMap(
mapType: MapType.normal,
initialCameraPosition: CameraPosition(
target: start_currentPostion,
zoom: 14,
),
onMapCreated: (GoogleMapController controller) {},
myLocationEnabled: true,
) : Container());
}
}

回答第二个

所以在你的GoogleMapPage中你只需要添加一个布尔值并根据位置

更新它

bool getLocationLoading;

在initState()中添加此值并将其设置为false，然后再次将此布尔变量调用到getLocation()方法并将其设置为true

@override
void initState() {
super.initState();
getLocation();
getLocationLoading = false;   // set false
}
getLocation() async {
var location = new Location();
location.onLocationChanged.listen((currentLocation) {
print(currentLocation.latitude);
print(currentLocation.longitude);
setState(() {
latLng =  LatLng(currentLocation.latitude, currentLocation.longitude);
});
print("getLocation:$latLng");
_onAddMarkerButtonPressed();
getLocationLoading = true;   // set true
});
}

然后简单地将您的GoogleMap添加到您的身体部位

body: getLocationLoading ? GoogleMap(
polylines: _polyLines,
markers: _markers,
mapType: MapType.normal,
initialCameraPosition: CameraPosition(
target: latLng,
zoom: 14,
),
onCameraMove: onCameraMove,
onMapCreated: (GoogleMapController controller) {
_controller.complete(controller);
},
myLocationEnabled: true,
), : Container());

Answer 2

我的代码如下:google_map.dart

import 'package:flutter/material.dart';
import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:location/location.dart';
import 'package:thehelpdesk/components/home/map_request.dart';
import 'package:thehelpdesk/widgets/appbar.dart';
import 'dart:async';
class GoogleMapPage extends StatefulWidget {
@override
_GoogleMapPageState createState() => _GoogleMapPageState();
}
class _GoogleMapPageState extends State<GoogleMapPage> {
Completer<GoogleMapController> _controller = Completer();
final Set<Marker> _markers = {};
static LatLng latLng;
LocationData currentLocation;
bool loading = true;
GoogleMapsServices _googleMapsServices = GoogleMapsServices();
final Set<Polyline> _polyLines = {};
Set<Polyline> get polyLines => _polyLines;
void _onAddMarkerButtonPressed() {
setState(() {
_markers.add(Marker(
markerId: MarkerId("111"),
position: latLng,
icon: BitmapDescriptor.defaultMarker,
));
});
}
getLocation() async {
var location = new Location();
location.onLocationChanged.listen((currentLocation) {
print(currentLocation.latitude);
print(currentLocation.longitude);
setState(() {
latLng =  LatLng(currentLocation.latitude, currentLocation.longitude);
});
print("getLocation:$latLng");
_onAddMarkerButtonPressed();
loading = false;
});
}
void onCameraMove(CameraPosition position) {
latLng = position.target;
}
@override
void initState() {
// setState(() {
//   getLocation();
// });
super.initState();
if(this.mounted) {
setState(() {
getLocation();
});
}
}
void sendRequest() async {
LatLng destination = LatLng(20.2961, 85.8245);
String route = await _googleMapsServices.getRouteCoordinates(
latLng, destination);
createRoute(route);
_addMarker(destination,"Bhubaneswar");
}
void createRoute(String encondedPoly) {
_polyLines.add(Polyline(
polylineId: PolylineId(latLng.toString()),
width: 4,
points: _convertToLatLng(_decodePoly(encondedPoly)),
color: Colors.red));
}
void _addMarker(LatLng location, String address) {
_markers.add(Marker(
markerId: MarkerId("112"),
position: location,
infoWindow: InfoWindow(title: address, snippet: "go here"),
icon: BitmapDescriptor.defaultMarker));
}
List<LatLng> _convertToLatLng(List points) {
List<LatLng> result = <LatLng>[];
for (int i = 0; i < points.length; i++) {
if (i % 2 != 0) {
result.add(LatLng(points[i - 1], points[i]));
}
}
return result;
}
List _decodePoly(String poly) {
var list = poly.codeUnits;
var lList = new List();
int index = 0;
int len = poly.length;
int c = 0;
do {
var shift = 0;
int result = 0;
do {
c = list[index] - 63;
result |= (c & 0x1F) << (shift * 5);
index++;
shift++;
} while (c >= 32);
if (result & 1 == 1) {
result = ~result;
}
var result1 = (result >> 1) * 0.00001;
lList.add(result1);
} while (index < len);
for (var i = 2; i < lList.length; i++) lList[i] += lList[i - 2];
print(lList.toString());
return lList;
}

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: aapBarSection('Google Map', Colors.blueAccent[700], context),
body: GoogleMap(
polylines: _polyLines,
markers: _markers,
mapType: MapType.normal,
initialCameraPosition: CameraPosition(
target: latLng,
zoom: 14,
),
onCameraMove: onCameraMove,
onMapCreated: (GoogleMapController controller) {
_controller.complete(controller);
},
myLocationEnabled: true,
),
floatingActionButton: FloatingActionButton.extended(
onPressed: () {
sendRequest();
},
label: Text('Destination'),
icon: Icon(Icons.directions),
),
);
}
}

map_request.dart

import 'package:google_maps_flutter/google_maps_flutter.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
const apiKey = "My API Key";
class GoogleMapsServices{
Future<String> getRouteCoordinates(LatLng l1, LatLng l2) async{
String url = "https://maps.googleapis.com/maps/api/directions/json?origin=${l1.latitude},${l1.longitude}&destination=${l2.latitude},${l2.longitude}&key=$apiKey";
http.Response response = await http.get(url);
Map values = jsonDecode(response.body);
print("====================>>>>>>>>$values");
return values["routes"][0]["overview_polyline"]["points"];
}
}