试试这个!

string temp="";

public void Initialize()
{
   FileSystemWatcher _fileWatcher = new FileSystemWatcher();
  _fileWatcher.Path = "C:\\Folder";
  _fileWatcher.NotifyFilter = NotifyFilters.LastWrite;
  _fileWatcher.Filter = "Version.txt";
  _fileWatcher.Changed += new FileSystemEventHandler(OnChanged);
  _fileWatcher.EnableRaisingEvents = true;
}

private void OnChanged(object source, FileSystemEventArgs e)
{
   .......
if(temp=="")
{
   //do thing you want.
   temp = e.name //name of text file.
}else if(temp !="" && temp != e.name)
{
   //do thing you want.
   temp = e.name //name of text file.
}else
{
  //second fire ignored.
}

}

这个解决方案适用于我的生产应用程序:

环境:

VB。Net Framework 4.5.2

手动设置对象属性:NotifyFilter = Size

然后使用下面的代码:

Public Class main
    Dim CalledOnce = False
    Private Sub FileSystemWatcher1_Changed(sender As Object, e As IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed
            If (CalledOnce = False) Then
                CalledOnce = True
                If (e.ChangeType = 4) Then
                    ' Do task...
                CalledOnce = False
            End If
        End Sub
End Sub

主要是为了未来的我:)

我用Rx写了一个包装器:

 public class WatcherWrapper : IDisposable
{
    private readonly FileSystemWatcher _fileWatcher;
    private readonly Subject<FileSystemEventArgs> _infoSubject;
    private Subject<FileSystemEventArgs> _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<FileSystemEventArgs>();
        _eventSubject = new Subject<FileSystemEventArgs>();

        Observable.FromEventPattern<FileSystemEventArgs>(_fileWatcher, "Changed").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);
        Observable.FromEventPattern<FileSystemEventArgs>(_fileWatcher, "Created").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);
        Observable.FromEventPattern<FileSystemEventArgs>(_fileWatcher, "Deleted").Select(e => e.EventArgs)
            .Subscribe(_infoSubject.OnNext);
        Observable.FromEventPattern<FileSystemEventArgs>(_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<FileSystemEventArgs> FileEvents => _eventSubject;


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

用法:

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)

恐怕这是FileSystemWatcher类的一个众所周知的错误/特性。这是来自类的文档:

You may notice in certain situations that a single creation event generates multiple Created events that are handled by your component. For example, if you use a FileSystemWatcher component to monitor the creation of new files in a directory, and then test it by using Notepad to create a file, you may see two Created events generated even though only a single file was created. This is because Notepad performs multiple file system actions during the writing process. Notepad writes to the disk in batches that create the content of the file and then the file attributes. Other applications may perform in the same manner. Because FileSystemWatcher monitors the operating system activities, all events that these applications fire will be picked up.

现在这段文本是关于Created事件的，但同样的事情也适用于其他文件事件。在一些应用程序中，您可能能够通过使用NotifyFilter属性来解决这个问题，但我的经验是，有时您还必须进行一些手动重复过滤(hacks)。

前段时间我书签了一个页面，里面有一些FileSystemWatcher技巧。你可能会想去看看。

以下是我的解决方案，帮助我阻止事件被提出两次:

watcher.NotifyFilter = NotifyFilters.FileName | NotifyFilters.Size;

这里我只设置了文件名和大小的NotifyFilter属性。 watcher是FileSystemWatcher的对象。希望这能有所帮助。

我简单地添加了一个dupe检查如下:

 private void OnChanged(object source, FileSystemEventArgs e)
    {
        string sTabName = Path.GetFileNameWithoutExtension(e.Name);
        string sLastLine = ReadLastLine(e.FullPath);
        if(sLastLine != _dupeCheck)
        {
            TabPage tp = tcLogs.TabPages[sTabName];
            TextBox tbLog = (TextBox)tp.Controls[0] as TextBox;

            tbLog.Invoke(new Action(() => tbLog.AppendText(sLastLine + Environment.NewLine)));
            tbLog.Invoke(new Action(() => tbLog.SelectionStart = tbLog.Text.Length));
            tbLog.Invoke(new Action(() => tbLog.ScrollToCaret()));
            _dupeCheck = sLastLine;
        }
    }

    public static String ReadLastLine(string path)
    {
        return ReadLastLine(path, Encoding.Default, "\n");
    }

    public static String ReadLastLine(string path, Encoding encoding, string newline)
    {
        int charsize = encoding.GetByteCount("\n");
        byte[] buffer = encoding.GetBytes(newline);
        using (FileStream stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
        {
            long endpos = stream.Length / charsize;
            for (long pos = charsize; pos < endpos; pos += charsize)
            {
                stream.Seek(-pos, SeekOrigin.End);
                stream.Read(buffer, 0, buffer.Length);
                if (encoding.GetString(buffer) == newline)
                {
                    buffer = new byte[stream.Length - stream.Position];
                    stream.Read(buffer, 0, buffer.Length);
                    return encoding.GetString(buffer);
                }
            }
        }
        return null;
    }

    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    private static extern int SendMessage(IntPtr hWnd, int wMsg, IntPtr wParam, IntPtr lParam);

    private const int WM_VSCROLL = 0x115;
    private const int SB_BOTTOM = 7;

    /// <summary>
    /// Scrolls the vertical scroll bar of a multi-line text box to the bottom.
    /// </summary>
    /// <param name="tb">The text box to scroll</param>
    public static void ScrollToBottom(TextBox tb)
    {
        SendMessage(tb.Handle, WM_VSCROLL, (IntPtr)SB_BOTTOM, IntPtr.Zero);
    }