Observable Collection and EmptyEnumerable

using System;

using System.Collections.Generic;namespace SPFControls {

    public class ObservableCollection<T>: IList<T> {

private List<T> items = new List<T>();

        public event NotifyCollectionChangedEventHandler<T> CollectionChanged;

public ObservableCollection() {

        }

public void Add(T item) {

            this.items.Add(item);

            this.FireCollectionChanged(NotifyCollectionChangedAction.Add, item);

        }

public void AddRange(IEnumerable<T> items) {

            this.items.AddRange(items);

            this.FireCollectionChanged(NotifyCollectionChangedAction.Add, items);

        }

public void Clear() {

            this.items.Clear();

            this.FireCollectionChanged(NotifyCollectionChangedAction.Reset, null);

        }

public bool Contains(T item) {

            return this.items.Contains(item);

        }

public void CopyTo(T[] array, int arrayIndex) {

            this.items.CopyTo(array, arrayIndex);

        }

public int Count {

            get { return this.items.Count; }

        }

public bool IsReadOnly {

            get { return false; }

        }

public bool Remove(T item) {

            bool removed = this.items.Remove(item);

            this.FireCollectionChanged(NotifyCollectionChangedAction.Remove, item);

            return removed;

        }

public T this[int index] {

            get { return this.items[index]; }

            set {

                this.FireCollectionChanged(NotifyCollectionChangedAction.Remove, this.items[index]);

                this.items[index] = value;

                this.FireCollectionChanged(NotifyCollectionChangedAction.Add, value);

            }

        }

public int IndexOf(T item) {

            return this.items.IndexOf(item);

        }

public void Insert(int index, T item) {

            this.items.Insert(index, item);

        }

public void RemoveAt(int index) {

            this.items.RemoveAt(index);

        }

public IEnumerator<T> GetEnumerator() {

            return this.items.GetEnumerator();

        }

System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {

            return this.items.GetEnumerator();

        }

protected void FireCollectionChanged(NotifyCollectionChangedAction action, IEnumerable<T> changedItems) {

            if (this.CollectionChanged != null)

                this.CollectionChanged(this, new NotifyCollectionChangedEventArgs<T>(action, changedItems));

        }

protected void FireCollectionChanged(NotifyCollectionChangedAction action, T changedItem) {

            if (this.CollectionChanged != null)

                this.CollectionChanged(this, new NotifyCollectionChangedEventArgs<T>(action, changedItem));

        }

    }

public delegate void NotifyCollectionChangedEventHandler<T>(object sender, NotifyCollectionChangedEventArgs<T> e);

public class NotifyCollectionChangedEventArgs<T>: EventArgs {

        private IList<T> changedItems;

        private NotifyCollectionChangedAction action;

public NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction action, IEnumerable<T> changedItems ) {

            this.action = action;

            List<T> changedList = new List<T>();

            if (changedItems != null)

                changedList.AddRange(changedItems);

            this.changedItems = changedList;

        }

public NotifyCollectionChangedEventArgs(NotifyCollectionChangedAction action, T changedItem) {

            this.action = action;

            this.changedItems = new List<T>();

            this.changedItems.Add(changedItem);

        }

public NotifyCollectionChangedAction Action {

            get { return this.action; }

        }

public IEnumerable<T> NewItems {

            get {

                if (this.action != NotifyCollectionChangedAction.Add)

                    return EmptyEnumerable<T>.Instance;

                return this.changedItems;

            }

        }

public IEnumerable<T> OldItems {

            get {

                if (this.action != NotifyCollectionChangedAction.Remove)

                    return EmptyEnumerable<T>.Instance;

                return this.changedItems;

            }

        }

}

public enum NotifyCollectionChangedAction {

        Add,

        Remove,

        Reset

    }

}

using System;

using System.Collections.Generic;namespace SPFControls {

    public class EmptyEnumerable<T> : IEnumerable<T>, IEnumerator<T> {

        private static EmptyEnumerable<T> instance = new EmptyEnumerable<T>();

protected EmptyEnumerable() {

        }

public IEnumerator<T> GetEnumerator() {

            return this;

        }

System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() {

            return this;

        }

public T Current {

            get { throw new ArgumentException(); }

        }

public void Dispose() {

        }

object System.Collections.IEnumerator.Current {

            get { throw new ArgumentException(); }

        }

public bool MoveNext() {

            return false;

        }

public void Reset() {

        }

public static EmptyEnumerable<T> Instance {

            get { return EmptyEnumerable<T>.instance; }

        }

    }

}