import com.firebase.geofire.GeoQuery; //导入依赖的package包/类
@Override
public void onCreate() {
    super.onCreate();
    Timber.tag(getClass().getSimpleName());
    Timber.d(getClass().getSimpleName() + " is creating");

    UserLocation currentLocation = CacheManager.pluck().getUserLocation();
    if (currentLocation == null) {
        currentLocation = new UserLocation();
        currentLocation.setLatitude(-7.76772);
        currentLocation.setLongitude(110.37863);
    }
    GeoLocation location = new GeoLocation(currentLocation.getLatitude(), currentLocation.getLongitude());

    GeoQuery query = FirebaseApi.pluck().userLocations().queryAtLocation(location, 20);

    CacheManager.pluck().listenUserLocation()
            .subscribe(userLocation -> {
                if (userLocation != null) {
                    GeoLocation newLocation = new GeoLocation(userLocation.getLatitude(),
                                                              userLocation.getLongitude());
                    query.setCenter(newLocation);
                }
            }, throwable -> {
                Timber.e(throwable.getMessage());
            });

    query.addGeoQueryEventListener(this);
}