file.java

// CALLING SERVICE FROM MAINACTIYITY:


Intent service = new Intent(SettingsActivity.this, ScreenService.class); 
//Changes - 1
if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O){
  //Changes -2 
      MainActivity.this.startForegroundService(mContext, service); 
   } else { 
      startService(service); 
   }

//ScreenService.java:

onCreate() {
    ''
      //Run only here and not on onStartCommand
      if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
           displayForeground()
        }
    ..
    ..
}

onStartCommand() {
    ''
   // displayForeground Notification
   return START_STICKY;
    ..
    ..
}

displayFroeground () {
 if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            startForeground(NOTIFICATION_ID, new Notification.Builder(this).build());
  }
  //if not Oreo and above do this.
  ......
}