集合为空时通知观察者

Question

I writing console application, and it has queue collection, that used as a factory of messages.

Is there some way that collection will raise events when it becames empty.

I just don't want start doing pulling it by myself, checking it from time to time.

I thought using ObservableCollection but I dont see a way to implement raising events when it's becomes empty.

Thanks for help.

Answer 1

ObservableCollection fires its CollectionChanged event when the contents of the collection change. Just hook that, and in your event handler, check to see if the collection's Count == 0 .

Answer 2

You could inherit from ObservableCollectionEx and add your own event:

    public class ObservableCollectionEx<T> : ObservableCollection<T>
    {
        public event EventHandler CollectionEmpty;

        protected override void OnCollectionChanged(NotifyCollectionChangedEventArgs e)
        {
            if (this.Count == 0)
            {
                var eventCopy = this.CollectionEmpty;
                if (eventCopy  != null)
                {
                    eventCopy(this, EventArgs.Empty);
                }
            }

            base.OnCollectionChanged(e);
        }
    }