public void RemoveHandStateChangeListener(HandStateChangeListener aListener)
 {
     lock (_handStateListenerLock)
     {
         if (this._handStateListeners.Contains(aListener))
             this._handStateListeners.Remove(aListener);
     }
 }
 public void AddHandStateChangeListener(HandStateChangeListener aListener)
 {
     lock (_handStateListenerLock)
     {
         if (!this._handStateListeners.Contains(aListener))
             this._handStateListeners.Add(aListener);
     }
 }