IObservable for file-change notifications

IOExtensions.cs

using System;
using System.IO;
using System.Reactive;
using System.Reactive.Disposables;
using System.Reactive.Linq;

/// <summary>
///     Extension methods for System.IO types.
/// </summary>
public static class IOExtensions
{
    /// <summary>
    ///     Observe any changes relating to a file.
    /// </summary>
    /// <param name="file">
    ///     The target file.
    /// </param>
    /// <param name="notificationFilters">
    ///     <see cref="NotifyFilters"/> indicating which types of notifications should be observed.
    /// </param>
    /// <returns>
    ///     An <see cref="IObservable{T}"/> sequence of <see cref="WatcherChangeTypes"/> values.
    /// </returns>
    public static IObservable<WatcherChangeTypes> ObserveChanges(this FileInfo file, NotifyFilters notificationFilters = NotifyFilters.Size)
    {
        return Observable.Create<WatcherChangeTypes>(subscriber =>
        {
            var disposal = new CompositeDisposable();
            var watcher = new FileSystemWatcher(file.DirectoryName)
            {
                Filter = file.Name,
                IncludeSubdirectories = false,
                NotifyFilter = NotifyFilters.Size // Only react when data is appended.
            };

            watcher.Changed += (sender, args) =>
            {
                if (args.FullPath != file.FullName)
                    return;

                file.Refresh();

                subscriber.OnNext(args.ChangeType);
            };
            watcher.Error += (sender, args) =>
            {
                subscriber.OnError(
                    args.GetException()
                );
            };

            disposal.Add(
                Disposable.Create(() =>
                {
                    subscriber.OnCompleted();
                })
            );

            watcher.EnableRaisingEvents = true;

            return disposal;
        });
    }
}