public void UnregisterSweepModeObserver(ISweepModeObserver ob)
 {
     if (ob != null && _sweepModeObs.Contains(ob))
     {
         _sweepModeObs.Remove(ob);
     }
 }
 public void RegisterSweepModeObserver(ISweepModeObserver ob)
 {
     if (ob != null && !_sweepModeObs.Contains(ob))
     {
         _sweepModeObs.Add(ob);
     }
 }