问如何以经度和经度为单位，计算出从一个点到另一个点的公路距离。颤动

EN

void getDistanceAndDuration(LatLng origin, LatLng destination, ResponseCallback<DistanceDurationResponse?, String?> callback) async {
    try {
      var apiResponse = await _client.get("https://maps.googleapis.com/maps/api/distancematrix/json?origins=${origin.latitude},${origin.longitude}"
          "&destinations=${destination.latitude},${destination.longitude}&key=$mapApiKey&mode=DRIVING&",);

      DistanceDurationResponse response = DistanceDurationResponse.fromJson(apiResponse.data);
      var rows = response?.rows;

      if(rows != null && rows.isNotEmpty) {
        var elements = rows.first.elements;

        if(elements != null && elements.isNotEmpty) {
          var element = elements.first;
          var duration = element.duration;
          var distance = element.distance;

        }
      }

    } on DioError catch (e) {
      log(e.toString());
    } on FormatException catch (e) {
      log(e.toString());
    } catch (e) {
      log(e.toString());
    }
  }

class DistanceDurationResponse {

  String? status;
  List<Rows>? rows;
  List<String>? originAddresses;
  List<String>? destinationAddresses;

  DistanceDurationResponse({
    this.destinationAddresses,
    this.originAddresses,
    this.rows,
    this.status,
  });

  DistanceDurationResponse.fromJson(dynamic json) {
    destinationAddresses = json['destination_addresses'] != null ? json['destination_addresses'].cast<String>() : [];
    originAddresses = json['origin_addresses'] != null ? json['origin_addresses'].cast<String>() : [];
    if (json['rows'] != null) {
      rows = [];
      json['rows'].forEach((v) {
        rows?.add(Rows.fromJson(v));
      });
    }
    status = json['status'];
  }

  Map<String, dynamic> toJson() {
    final map = <String, dynamic>{};
    map['destination_addresses'] = destinationAddresses;
    map['origin_addresses'] = originAddresses;
    if (rows != null) {
      map['rows'] = rows?.map((v) => v.toJson()).toList();
    }
    map['status'] = status;
    return map;
  }
}

class Rows {
  List<DistanceDurationElement>? elements;

  Rows({this.elements,});

  Rows.fromJson(dynamic json) {
    if (json['elements'] != null) {
      elements = [];
      json['elements'].forEach((v) {
        elements?.add(DistanceDurationElement.fromJson(v));
      });
    }
  }

  Map<String, dynamic> toJson() {
    final map = <String, dynamic>{};
    if (elements != null) {
      map['elements'] = elements?.map((v) => v.toJson()).toList();
    }
    return map;
  }
}

class DistanceDurationElement {

  String? status;
  EstimatedDistance? distance;
  EstimatedDuration? duration;

  DistanceDurationElement({
    this.distance,
    this.duration,
    this.status,
  });

  DistanceDurationElement.fromJson(dynamic json) {
    distance = json['distance'] != null ? EstimatedDistance.fromJson(json['distance']) : null;
    duration = json['duration'] != null ? EstimatedDuration.fromJson(json['duration']) : null;
    status = json['status'];
  }

  Map<String, dynamic> toJson() {
    final map = <String, dynamic>{};
    if (distance != null) {
      map['distance'] = distance?.toJson();
    }
    if (duration != null) {
      map['duration'] = duration?.toJson();
    }
    map['status'] = status;
    return map;
  }
}

class EstimatedDuration {

  int? value;
  String? text;

  EstimatedDuration({
    this.text,
    this.value,
  });

  EstimatedDuration.fromJson(dynamic json) {
    text = json['text'];
    value = json['value'];
  }

  Map<String, dynamic> toJson() {
    final map = <String, dynamic>{};
    map['text'] = text;
    map['value'] = value;
    return map;
  }
}

class EstimatedDistance {

  int? value;
  String? text;

  EstimatedDistance({
    this.text,
    this.value,
  });

  EstimatedDistance.fromJson(dynamic json) {
    text = json['text'];
    value = json['value'];
  }

  Map<String, dynamic> toJson() {
    final map = <String, dynamic>{};
    map['text'] = text;
    map['value'] = value;
    return map;
  }
}