public class ServiceNotification extends Service {

DatabaseReference reference;

SharedPreferences preferences;

private NotificationManager notificationManager;
private final static String CHANNEL_ID="NOTIFICACION";
private final static int NOTIFICACION_ID=0;
private PendingIntent pendingIntent;

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

    // Crea la notificación y a que Activity quiero ir
    setPendingIntent();
    sendNotification();

}


public int onStartCommand(Intent intent, int flags, int startId){
  return START_STICKY;
}

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


private void setPendingIntent(){
    Intent intent=new Intent(this, RecibirDelito.class);
    TaskStackBuilder stackBuilder= TaskStackBuilder.create(this);
    stackBuilder.addParentStack(RecibirDelito.class);
    stackBuilder.addNextIntent(intent);
    pendingIntent=stackBuilder.getPendingIntent(1,PendingIntent.FLAG_UPDATE_CURRENT);
}



private void sendNotification() {

   // Consulta la base de datos
    reference= FirebaseDatabase.getInstance().getReference();
    Query query = reference.child("delito");

    // Evento cuando escucha si se añadió un nuevo delito
    query.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

           // Construye la notificación cuando se agrega un nuevo delito
            if (Build.VERSION.SDK_INT>=Build.VERSION_CODES.O){
                    CharSequence name="Notifacion";
                    NotificationChannel notificationChannel= new NotificationChannel(CHANNEL_ID,name,NotificationManager.IMPORTANCE_DEFAULT);
                    notificationManager =(NotificationManager)getSystemService(NOTIFICATION_SERVICE);
                    notificationManager.createNotificationChannel(notificationChannel);

                }

                NotificationCompat.Builder builder= new NotificationCompat.Builder(getApplicationContext(),CHANNEL_ID);
                builder.setSmallIcon(R.drawable.ic_android_black_24dp);
                builder.setContentTitle("Emergencia");
                builder.setContentText("Nueva emergencia");
                builder.setColor(Color.BLUE);
                builder.setPriority(NotificationCompat.PRIORITY_DEFAULT);
                builder.setLights(Color.MAGENTA,1000,1000);
                builder.setVibrate(new long[]{1000,1000,});
                builder.setDefaults(Notification.DEFAULT_SOUND);

                builder.setContentIntent(pendingIntent);

                NotificationManagerCompat notificationManagerCompat = NotificationManagerCompat.from(getApplicationContext());
                notificationManagerCompat.notify(NOTIFICACION_ID,builder.build());


        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

    });


}