FileSystemWatcher Changed event is raised twice

Question

I have an application where I am looking for a text file and if there are any changes made to the file I am using the OnChanged eventhandler to handle the event

Answer 1

mostly for future me :)

I wrote a wrapper using Rx:

 public class WatcherWrapper : IDisposable
{
    private readonly FileSystemWatcher _fileWatcher;
    private readonly Subject _infoSubject;
    private Subject _eventSubject;

    public WatcherWrapper(string path, string nameFilter = "*.*", NotifyFilters? notifyFilters = null)
    {
        _fileWatcher = new FileSystemWatcher(path, nameFilter);

        if (notifyFilters != null)
        {
            _fileWatcher.NotifyFilter = notifyFilters.Value;
        }

        _infoSubject = new Subject();
        _eventSubject = new Subject();

        Observable.FromEventPattern(_fileWatcher, "Changed").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);
        Observable.FromEventPattern(_fileWatcher, "Created").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);
        Observable.FromEventPattern(_fileWatcher, "Deleted").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);
        Observable.FromEventPattern(_fileWatcher, "Renamed").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);

        // this takes care of double events and still works with changing the name of the same file after a while
        _infoSubject.Buffer(TimeSpan.FromMilliseconds(20))
            .Select(x => x.GroupBy(z => z.FullPath).Select(z => z.LastOrDefault()).Subscribe(
                infos =>
                {
                    if (infos != null)
                        foreach (var info in infos)
                        {
                            {
                                _eventSubject.OnNext(info);
                            }
                        }
                });

        _fileWatcher.EnableRaisingEvents = true;
    }

    public IObservable FileEvents => _eventSubject;


    public void Dispose()
    {
        _fileWatcher?.Dispose();
        _eventSubject.Dispose();
        _infoSubject.Dispose();
    }
}

Usage:

var watcher = new WatcherWrapper(_path, "*.info");
// all more complicated and scenario specific filtering of events can be done here    
watcher.FileEvents.Where(x => x.ChangeType != WatcherChangeTypes.Deleted).Subscribe(x => //do stuff)