In my case need to get the last line of a text file that is inserted by other application, as soon as insertion is done. Here is my solution. When the first event is raised, i disable the watcher from raising others, then i call the timer TimeElapsedEvent because when my handle function OnChanged is called i need the size of the text file, but the size at that time is not the actual size, it is the size of the file imediatelly before the insertion. So i wait for a while to proceed with the right file size.

private FileSystemWatcher watcher = new FileSystemWatcher();
...
watcher.Path = "E:\\data";
watcher.NotifyFilter = NotifyFilters.LastWrite ;
watcher.Filter = "data.txt";
watcher.Changed += new FileSystemEventHandler(OnChanged);
watcher.EnableRaisingEvents = true;

...

private void OnChanged(object source, FileSystemEventArgs e)
   {
    System.Timers.Timer t = new System.Timers.Timer();
    try
    {
        watcher.Changed -= new FileSystemEventHandler(OnChanged);
        watcher.EnableRaisingEvents = false;

        t.Interval = 500;
        t.Elapsed += (sender, args) => t_Elapsed(sender, e);
        t.Start();
    }
    catch(Exception ex) {
        ;
    }
}

private void t_Elapsed(object sender, FileSystemEventArgs e) 
   {
    ((System.Timers.Timer)sender).Stop();
       //.. Do you stuff HERE ..
     watcher.Changed += new FileSystemEventHandler(OnChanged);
     watcher.EnableRaisingEvents = true;
}

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。

好吧，这是我如何只引发一个事件的解决方案:

FileSystemWatcheк watcher = new FileSystemWatcher();

//'path' - path to the file that has been modified.
watcher.Changed += (s, e) => FileChanged(path);

这里是FileChanged实现

//count is our counter to triger when we can raise and when not.
private int count = 0;
private void FileChanged(string path)
{
   if (count % 2 == 0)
     {
       //code here
     }

     count ++;
}

我的场景是，我有一个虚拟机，其中有一个Linux服务器。我正在Windows主机上开发文件。当我在主机上的一个文件夹中更改某些内容时，我希望所有的更改都被上传，并通过Ftp同步到虚拟服务器上。这是我如何消除重复更改事件当我写入一个文件(这标志着包含文件要修改的文件夹):

private Hashtable fileWriteTime = new Hashtable();

private void fsw_sync_Changed(object source, FileSystemEventArgs e)
{
    string path = e.FullPath.ToString();
    string currentLastWriteTime = File.GetLastWriteTime( e.FullPath ).ToString();

    // if there is no path info stored yet
    // or stored path has different time of write then the one now is inspected
    if ( !fileWriteTime.ContainsKey(path) ||
         fileWriteTime[path].ToString() != currentLastWriteTime
    )
    {
        //then we do the main thing
        log( "A CHANGE has occured with " + path );

        //lastly we update the last write time in the hashtable
        fileWriteTime[path] = currentLastWriteTime;
    }
}

我主要创建一个哈希表来存储文件写时间信息。然后，如果哈希表有被修改的文件路径，并且它的时间值与当前通知的文件更改相同，那么我就知道它是事件的副本，并忽略它。

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。

我已经用一个类创建了一个Git repo，该类扩展了FileSystemWatcher，以便仅在复制完成时触发事件。它将丢弃除最后一个事件以外的所有已更改事件，仅在文件可读时才引发该事件。

下载FileSystemSafeWatcher并将其添加到项目中。

然后将其用作普通的FileSystemWatcher并在事件触发时进行监视。

var fsw = new FileSystemSafeWatcher(file);
fsw.EnableRaisingEvents = true;
// Add event handlers here
fsw.Created += fsw_Created;