LibGDX - check if compass needs calibration

How to check if compass is calibrated well in LibGDX (on Android). I've found how to do it on native Android:

In Android can I programmatically detect that the compass is not yet calibrated?

But couldn't find if that's implemented in LibGDX.

What you want is described in the wiki article Interfacing with platform specific code. LibGDX doesn't have any functionality for it because it isn't common and it doesn't make any sense for other backends.

In the core module you'll have something like this:

public interface GameListener {
    void calibrateCompassIfNeeded()
}

public class Application extends ApplicationAdapter {

    private GameListener listener;    

    public Application(GameListener listener) {
        this.listener = listener;
    }

    @Override
    public void create() {
        // Call listener.calibrateCompassIfNeeded() whenever needed.
    }

    public void onCompassChanged(float[] values) {
        // Do something...
    }
}

And in the android module:

public class AndroidLauncher extends AndroidApplication implements GameListener, SensorEventListener {
    private static final int COMPASS_ACCURACY_UNKNOWN = -1;

    private Application app;
    private int compassAccuracy = COMPASS_ACCURACY_UNKNOWN;

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

        SensorManager sensorManager = (SensorManager) getSystemService(Context.SENSOR_SERVICE);
        Sensor compassSensor = sensorManager.getDefaultSensor(Sensor.TYPE_MAGNETIC_FIELD);
        sensorManager.registerListener(this, compassSensor, SensorManager.SENSOR_DELAY_GAME)

        AndroidApplicationConfiguration config = new AndroidApplicationConfiguration();
        app = new Application(this);
        initialize(app, config);
    }

    @Override
    public void calibrateCompassIfNeeded() {
        if (compassAccuracy != COMPASS_ACCURACY_UNKNOWN && compassAccuracy < SENSOR_STATUS_ACCURACY_MEDIUM) {
            // Calibrate only if accuracy is below medium.
            // Show whatever is needed so user calibrates the compass.
        }
    }

    @Override
    public void onSensorChanged(SensorEvent event) {
        if (event.sensor.getType() == Sensor.TYPE_MAGNETIC_FIELD) {
            app.onCompassChanged(event.values);
        }
    }

    @Override
    public void onAccuracyChanged(Sensor sensor, int accuracy) {
       compassAccuracy = accuracy;
    }
}

I haven't tried it and I have never used the compass before but I'm pretty sure this will work fine.