You are probably being hampered by the restrictions brought in with Android 8 (API 26) which limits the frequency that background apps can retrieve the current location.

This was brought in to save battery but it means that you will need to have a visible notification in order for Android to consider the app as being in the foreground. Otherwise it will only retrieve the location a few times per hour whilst the app is in the background.

https://developer.android.com/about/versions/oreo/background-location-limits gives you some further background (excuse the pun) information.

I am using below code to get the track the location of user.
This works proper when my application in foreground. But when my application move to background it stop working and i can not get any location.

import 'dart:async';
import 'package:permission_handler/permission_handler.dart';
import 'package:geolocator/geolocator.dart';

class FetchLocation   {
  var geolocator = Geolocator();
  var locationOptions = LocationOptions(accuracy: LocationAccuracy.high, distanceFilter: 10,forceAndroidLocationManager: true,timeInterval: 1);
  void trackGeoLocation()async{
    final PermissionStatus permission = await PermissionHandler()
        .checkPermissionStatus(PermissionGroup.location);
      if(permission == PermissionStatus.granted){
        fetchLocation();
      }else{
        askPermission();
      }

  }
  void askPermission() {
    PermissionHandler().requestPermissions([PermissionGroup.locationAlways]).then(__onStatusRequested);
  }
  void __onStatusRequested(Map<PermissionGroup, PermissionStatus> statuses){
    final status = statuses[PermissionGroup.locationWhenInUse];

    print(status);
    if(status == PermissionStatus.restricted || status == PermissionStatus.neverAskAgain){
    } else if(status == PermissionStatus.denied){
      askPermission();
    }else{
      fetchLocation();
    }
  }
  void fetchLocation(){
    StreamSubscription<Position> positionStream = geolocator.getPositionStream(locationOptions).listen(
            (Position position) {
          print(position == null ? 'Unknown' : position.latitude.toString() + ', ' + position.longitude.toString());
        });
  }
}