code: protected void beforeLoading()
      {
          if (_listeners != null)
          {
              CollectionProxyListener listener;
  
              if (_perThreadDescriptorsEnabled) {
                  loadProfileIfNeeded();
              }
              for (int idx = _listeners.size() - 1; idx >= 0; idx--)
              {
                  listener = (CollectionProxyListener)_listeners.get(idx);
                  listener.beforeLoading(this);
              }
          }
      }
docs: Notifies all listeners that the data is about to be loaded.