/// <summary>
/// Adds a weak event listener for a CollectionChanged event.
/// </summary>
/// <param name="source">The source of the event.</param>
/// <param name="handler">The event handler.</param>
/// <exception cref="ArgumentNullException">source must not be <c>null</c>.</exception>
/// <exception cref="ArgumentNullException">handler must not be <c>null</c>.</exception>
protected void AddWeakEventListener(INotifyCollectionChanged source, NotifyCollectionChangedEventHandler handler)
{
if (source == null) { throw new ArgumentNullException("source"); }
if (handler == null) { throw new ArgumentNullException("handler"); }
CollectionChangedEventListener listener = new CollectionChangedEventListener(source, handler);
collectionChangedListeners.Add(listener);
CollectionChangedEventManager.AddListener(source, listener);
}