Flutter - Looping through a list of latitude and longitude from rest api to get distance between two coordinates

问题

In my code being able to successfully get the distance between the two coordinate (lAT and LNG) but my listview returns the value for only one of the list of values. Kindly find my code below.

String lat = "";
String lng = "";
Double distanceInKilometers = "";

Future getDistance() async {

    distanceInMeters = await Geolocator().distanceBetween(
        currentLocation.latitude, currentLocation.longitude, double.parse(lat), double.parse(lng));

    distanceInKilometers = distanceInMeters.toInt() / 1000;

    }


ListView.separated( itemCount: content.length,
                     itemBuilder: (context, position) {
                                      lat = content[position].lat;
                                      lng = content[position].lng;

                      return Container(
child: Column(
children: <Widget>[
new Text(distanceInKilometers.toString())

],),

))

回答1:

I have seen multiple mistake in your code.

First, your code is not compiling

Double type is lowercase in Dart language.
You should not initialize a double variable with an empty String.

Second, you use global states with async calls. It would be better, if you just pass parameters into getDistance method. Like this:

Future<double> getDistance(double lat, double long) async {
  final distanceInMeters = await Geolocator().distanceBetween(
        currentLocation.latitude,
        currentLocation.longitude,
        lat,
        lng
  );

  return distanceInMeters / 1000;
}

Finally you should use a FutureBuilder to call getDistance:

ListView.separated(
  itemCount: content.length,
  separatorBuilder: (context, position) {
   // return a separator widget;
  },
  itemBuilder: (context, position) {
    final current = content[position];
    return FutureBuilder<String>(
      future: getDistance(current.lat, current.long)
                   .then((value) => value.toString()),
      builder: (context, snapshot) {
        return Container(
          child: Column(
            children: <Widget>[new Text(snapshot.data)],
          ),
        );
     });
});

来源：https://stackoverflow.com/questions/60994455/flutter-looping-through-a-list-of-latitude-and-longitude-from-rest-api-to-get

标签

dictionary

listview

Flutter

distance