//subscription mechanism
 public void CustomizedSubscribe(MappingUpdateSubscriber <T> aSubscription)
 {
     subscription = aSubscription;
     subscription.AttachTo(this);
 }
 public void Subscribe(Control aSubject, bool aAllowNulls, ListControlMapping aListMapping)
 {
     subscription = new MappingUpdateSubscriber <T>(this, aSubject, aAllowNulls, aListMapping);
 }