LocationService.java

package com.codingwithmitch.googlemaps2018.services;

import android.Manifest;
import android.app.Notification;
import android.app.NotificationChannel;
import android.app.NotificationManager;
import android.app.Service;
import android.content.Context;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.location.Location;

import android.os.Build;
import android.os.IBinder;
import android.os.Looper;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.NotificationCompat;
import android.util.Log;

import com.codingwithmitch.googledirectionstest.R;
import com.codingwithmitch.googledirectionstest.UserClient;
import com.codingwithmitch.googledirectionstest.models.User;
import com.codingwithmitch.googledirectionstest.models.UserLocation;
import com.google.android.gms.location.FusedLocationProviderClient;
import com.google.android.gms.location.LocationCallback;
import com.google.android.gms.location.LocationRequest;
import com.google.android.gms.location.LocationResult;
import com.google.android.gms.location.LocationServices;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.firestore.DocumentReference;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.GeoPoint;

public class LocationService extends Service {

    private static final String TAG = "LocationService";

    private FusedLocationProviderClient mFusedLocationClient;
    private final static long UPDATE_INTERVAL = 4 * 1000;  /* 4 secs */
    private final static long FASTEST_INTERVAL = 2000; /* 2 sec */

    @Nullable
    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onCreate() {
        super.onCreate();

        mFusedLocationClient = LocationServices.getFusedLocationProviderClient(this);

        if (Build.VERSION.SDK_INT >= 26) {
            String CHANNEL_ID = "my_channel_01";
            NotificationChannel channel = new NotificationChannel(CHANNEL_ID,
                    "My Channel",
                    NotificationManager.IMPORTANCE_DEFAULT);

            ((NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE)).createNotificationChannel(channel);

            Notification notification = new NotificationCompat.Builder(this, CHANNEL_ID)
                    .setContentTitle("")
                    .setContentText("").build();

            startForeground(1, notification);
        }
    }

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d(TAG, "onStartCommand: called.");
        getLocation();
        return START_NOT_STICKY;
    }

private void getLocation() {

        // ---------------------------------- LocationRequest ------------------------------------
        // Create the location request to start receiving updates
        LocationRequest mLocationRequestHighAccuracy = new LocationRequest();
        mLocationRequestHighAccuracy.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        mLocationRequestHighAccuracy.setInterval(UPDATE_INTERVAL);
        mLocationRequestHighAccuracy.setFastestInterval(FASTEST_INTERVAL);
        

        // new Google API SDK v11 uses getFusedLocationProviderClient(this)
        if (ActivityCompat.checkSelfPermission(this,
                Manifest.permission.ACCESS_FINE_LOCATION) != PackageManager.PERMISSION_GRANTED) {
            Log.d(TAG, "getLocation: stopping the location service.");
            stopSelf();
            return;
        }
        Log.d(TAG, "getLocation: getting location information.");
        mFusedLocationClient.requestLocationUpdates(mLocationRequestHighAccuracy, new LocationCallback() {
                    @Override
                    public void onLocationResult(LocationResult locationResult) {

                        Log.d(TAG, "onLocationResult: got location result.");

                        Location location = locationResult.getLastLocation();

                        if (location != null) {
                            User user = ((UserClient)(getApplicationContext())).getUser();
                            GeoPoint geoPoint = new GeoPoint(location.getLatitude(), location.getLongitude());
                            UserLocation userLocation = new UserLocation(user, geoPoint, null);
                            saveUserLocation(userLocation);
                        }
                    }
                },
                Looper.myLooper()); // Looper.myLooper tells this to repeat forever until thread is destroyed
    }

    private void saveUserLocation(final UserLocation userLocation){

        try{
            DocumentReference locationRef = FirebaseFirestore.getInstance()
                    .collection(getString(R.string.collection_user_locations))
                    .document(FirebaseAuth.getInstance().getUid());

            locationRef.set(userLocation).addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    if(task.isSuccessful()){
                        Log.d(TAG, "onComplete: \ninserted user location into database." +
                                "\n latitude: " + userLocation.getGeo_point().getLatitude() +
                                "\n longitude: " + userLocation.getGeo_point().getLongitude());
                    }
                }
            });
        }catch (NullPointerException e){
            Log.e(TAG, "saveUserLocation: User instance is null, stopping location service.");
            Log.e(TAG, "saveUserLocation: NullPointerException: "  + e.getMessage() );
            stopSelf();
        }

    }




}

MainActivity.java

    private void startLocationService(){
        if(!isLocationServiceRunning()){
            Intent serviceIntent = new Intent(this, LocationService.class);
//        this.startService(serviceIntent);

            if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O){

                MainActivity.this.startForegroundService(serviceIntent);
            }else{
                startService(serviceIntent);
            }
        }
    }

    private boolean isLocationServiceRunning() {
        ActivityManager manager = (ActivityManager) getSystemService(ACTIVITY_SERVICE);
        for (ActivityManager.RunningServiceInfo service : manager.getRunningServices(Integer.MAX_VALUE)){
            if("com.codingwithmitch.googledirectionstest.services.LocationService".equals(service.service.getClassName())) {
                Log.d(TAG, "isLocationServiceRunning: location service is already running.");
                return true;
            }
        }
        Log.d(TAG, "isLocationServiceRunning: location service is not running.");
        return false;
    }

@mitchtabian, this is so cool