NotifyCollectionChangedEventArgs.cs

public class NotifyCollectionChangedEventArgs<T>
{
    private readonly NotifyCollectionChangedEventArgs _args;

    public NotifyCollectionChangedEventArgs(NotifyCollectionChangedEventArgs args)
    {
        _args = args;
    }

    public IEnumerable<T> NewItems => _args.NewItems?.Cast<T>() ?? Enumerable.Empty<T>();

    public int NewStartingIndex => _args.NewStartingIndex;

    public IEnumerable<T> OldItems => _args.OldItems?.Cast<T>() ?? Enumerable.Empty<T>();

    public int OldStartingIndex => _args.OldStartingIndex;

    public NotifyCollectionChangedAction Action => _args.Action;
}