无法找到当前位置和目标位置之间的距离

Question

我被困在处理未来和从 Firebase 提取地址并显示在标记上的距离上， 虽然我已经设法编写了一些代码来获取当前用户位置、计算距离并将地址转换为 LatLng，但我仍然面临困难。

下面我附上了我的代码，并突出显示了我要计算距离的位置（内部小部件 setMapPins()）

我已将地址存储在收藏店内，并将名为 Address 的文档存储在 firebase 中

请帮助我计算 Streambuilder 内的距离并将其显示在标记上。提前致谢。

这是我完整的map.dart 文件中的link

'necessary imports'
'necessary initialization'

  _getCurrentLocation() async {
    await _geolocator
        .getCurrentPosition(desiredAccuracy: LocationAccuracy.high)
        .then((Position position) async {
      setState(() {
        _currentPosition = position;
        sourceLocation =
            LatLng(_currentPosition.latitude, _currentPosition.longitude);
        print('CURRENT POS: $_currentPosition');
        mapController.animateCamera(
          CameraUpdate.newCameraPosition(
            CameraPosition(
              target: LatLng(position.latitude, position.longitude),
              zoom: 14.0,
            ),
          ),
        );
      });
      await _getAddress();
    }).catchError((e) {
      print(e);
    });
  }

  // Method for retrieving the address
  _getAddress() async {
    try {
      List<Placemark> p = await _geolocator.placemarkFromCoordinates(
          _currentPosition.latitude, _currentPosition.longitude);

      Placemark place = p[0];

      setState(() {
        _currentAddress =
            "${place.name}, ${place.locality}, ${place.postalCode}, ${place.country}";
        startAddressController.text = _currentAddress;
        _startAddress = _currentAddress;
      });
    } catch (e) {
      print(e);
    }
  }

  // Method for calculating the distance between two places
  Future<bool> _calculateDistance() async {
    try {
      // Retrieving placemarks from addresses
      List<Placemark> startPlacemark =
          await _geolocator.placemarkFromAddress(_startAddress);
      List<Placemark> destinationPlacemark =
          await _geolocator.placemarkFromAddress(_destinationAddress);

      if (startPlacemark != null && destinationPlacemark != null) {

        Position startCoordinates = _startAddress == _currentAddress
            ? Position(
                latitude: _currentPosition.latitude,
                longitude: _currentPosition.longitude)
            : startPlacemark[0].position;
        Position destinationCoordinates = destinationPlacemark[0].position;

        await _createPolylines(startCoordinates, destinationCoordinates);

        double totalDistance = 0.0;

        // Calculating the total distance by adding the distance
        // between small segments
        for (int i = 0; i < polylineCoordinates.length - 1; i++) {
          totalDistance += _coordinateDistance(
            polylineCoordinates[i].latitude,
            polylineCoordinates[i].longitude,
            polylineCoordinates[i + 1].latitude,
            polylineCoordinates[i + 1].longitude,
          );
        }

        setState(() {
          _placeDistance = totalDistance.toStringAsFixed(2);
        return true;
      }
    } catch (e) {
      print(e);
    }
    return false;
  }
 // formula

  double _coordinateDistance(lat1, lon1, lat2, lon2) {
    var p = 0.017453292519943295;
    var c = cos;
    var a = 0.5 -
        c((lat2 - lat1) * p) / 2 +
        c(lat1 * p) * c(lat2 * p) * (1 - c((lon2 - lon1) * p)) / 2;
    return 12742 * asin(sqrt(a));
  }

  // Create the polylines for showing the route between two places
  _createPolylines(start, destination) async {
    polylinePoints = PolylinePoints();
    List<PointLatLng> result = await polylinePoints.getRouteBetweenCoordinates(
      googleAPIKey, // Google Maps API Key
      start.latitude, start.longitude,
      destination.latitude, destination.longitude,
    );

    if (result.isNotEmpty) {
      result.forEach((PointLatLng point) {
        polylineCoordinates.add(LatLng(point.latitude, point.longitude));
      });
    }
  }

  Widget setMapPins() {

    return StreamBuilder(
        stream: Firestore.instance.collection('shops').snapshots(),
        builder: (context, snapshot) {
          if (!snapshot.hasData) return Text('Loading maps... Please Wait');
          for (int i = 0; i < snapshot.data.documents.length; i++) {
            print(snapshot.data.documents[i]);


         ///  here i want to calculate distance by extracting address from Firebase and then displaying on marker 

          }
          return Container();
        });
  }


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

Answer 1

为了降低代码的复杂度，您可以使用此函数计算两点之间的距离。（..在 GeoLocator 包中）

double distanceInMeters =Geolocator().distanceBetween(lat1, long1,lat2,long2);

更新 2：-

创建一个函数来执行异步任务，

var distInMeters;

getDist({var latt,var longg}) async{


distanceInMeters = await Geolocator().distanceBetween(latt, longg,lat2,long2);// lat2 and long2 are global variables with current user's location


}

在您的 Streambuilder 中，

StreamBuilder(
    stream: Firestore.instance.collection('shops').snapshots(),
    builder: (BuildContext context,
        AsyncSnapshot<List<DocumentSnapshot>> snapshots) {
      if (snapshots.connectionState == ConnectionState.active &&
          snapshots.hasData) {
        print(snapshots.data);
        return ListView.builder(
          itemCount: snapshots.data.length,
          itemBuilder: (BuildContext context, int index) {
            DocumentSnapshot doc = snapshots.data[index];
Map yourdata= doc.data; 
/*
Here, you can get latitude and longitude from firebase, using keys,based on your document structure.
Example, var lat=yourdata["latitude"];
var long=yourdata["longitude"];

Now, you can calculate the distance,

getDist(latt:lat,longg:long);

 here lat2 and long2 are current user's latitude and longitude.
print(distInMeters);
*/
            return Text("please upvote and accept this as the answer if it helped :) "),
            );
          },
        );
      } else {
        return Center(child: CircularProgressIndicator());
      }
    },
  ),