Cancelable Collection

Question

I'm trying to implement a collection class (either derived from ObservableCollection or BindingList) that will allow me to cancel the addition of any new item as it happens.

Now I know ObservableCollection does not allow the editing of items in the collection during the CollectionChanged event for a reason but I'm looking for a way to 'bypass' this either by deriving from ObservableCollection or BindingList.

Any examples will be appreciated.

Answer 1

Well, you would need some BeforeCollectionChanged event, pass an EventArgs with a Cancelled property which you look at to determine whether to add it or not.

Kinda like this, I guess:

public override void Add(T item) {
  var e = new BeforeCollectionChangedEventArgs();
  RaiseBeforeCollectionChanged(e);
  if (!e.Canceled)
    base.Add(item);
}

CollectionChanged is obviously too late because by then the collection already has been changed.