public void registerChangeListener(final Object lifecycleRef, final Consumer<PersistableFolder> listener) {
        List<Consumer<PersistableFolder>> listeners = changeListeners.get(lifecycleRef);
        if (listeners == null) {
            listeners = new ArrayList<>();
            changeListeners.put(lifecycleRef, listeners);
        }
        listeners.add(listener);
    }
registers a listener which is fired each time the actual location of this folder changes
main/src/main/java/cgeo/geocaching/storage/PersistableFolder.java