自定義 LiveData

如果需要自定義邏輯，可以編寫自定義 LiveData。
不要編寫自定義類，如果只需要轉換資料（使用 Transformations 類）

public class LocationLiveData extends LiveData<Location> {
    private LocationManager locationManager;
    
    private LocationListener listener = new LocationListener() {
        @Override
        public void onLocationChanged(Location location) {
            setValue(location);
        }

        @Override
        public void onStatusChanged(String provider, int status, Bundle extras) {
            // Do something
        }

        @Override
        public void onProviderEnabled(String provider) {
            // Do something
        }

        @Override
        public void onProviderDisabled(String provider) {
            // Do something
        }
    };

    public LocationLiveData(Context context) {
        locationManager = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
    }

    @Override
    protected void onActive() {
        // We have observers, start working
        locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, listener);
    }

    @Override
    protected void onInactive() {
        // We have no observers, stop working
        locationManager.removeUpdates(listener);
    }
}