Why is my native android code in Flutter showing errors?

I am testing platform specific coding with Flutter. I opened the android folder in Android Studio, wrote my code and it shows no errors. I then moved back to Flutter which is underlining in red the Rs in the code below. However, the app is working fine. I am wondering why an error is showing and what I can do to remove these red lines. I would be grateful for pointers.

Here is my code:

public class MyTileService extends TileService {

private final int STATE_ON = 1;
private final int STATE_OFF = 0;
private int toggleState = STATE_ON;


@Override
public void onTileAdded() {
    System.out.println("onTileAdded");
}

@Override
public void onTileRemoved() {
    System.out.println("onTileRemoved");
}

@Override
public void onStartListening() {
    System.out.println("onStartListening");
}

@Override
public void onStopListening() {
    System.out.println("onStopListening");
}

@Override
public void onClick() {
    System.out.println("onClick state = " + Integer.toString(getQsTile().getState()));
    Icon icon;
    if (toggleState == STATE_ON) {
        toggleState = STATE_OFF;
        icon = Icon.createWithResource(getApplicationContext(), R.drawable.ic_spa_black_24dp);
        System.out.println("OFF");
    } else {
        toggleState = STATE_ON;
        icon = Icon.createWithResource(getApplicationContext(), R.drawable.ic_star_border_black_24dp);
        System.out.println("ON");
    }
    getQsTile().setIcon(icon);
    getQsTile().updateTile();
}

}

I tried cleaning the android project, uninstalling and reinstalling Flutter and Dart plugins, checking flutter doctor.

Here is an image: