事件如果没有问，这是一个遗憾，没有现成的解决方案样本f#。 要解决这个问题，这里有我的方法，因为我可以，而且f#是一种很棒的。net语言。

使用FSharp.Control.Reactive包过滤掉重复的事件，它只是响应式扩展的f#包装器。所有这些都可以针对全框架或netstandard2.0:

let createWatcher path filter () =
    new FileSystemWatcher(
        Path = path,
        Filter = filter,
        EnableRaisingEvents = true,
        SynchronizingObject = null // not needed for console applications
    )

let createSources (fsWatcher: FileSystemWatcher) =
    // use here needed events only. 
    // convert `Error` and `Renamed` events to be merded
    [| fsWatcher.Changed :> IObservable<_>
       fsWatcher.Deleted :> IObservable<_>
       fsWatcher.Created :> IObservable<_>
       //fsWatcher.Renamed |> Observable.map renamedToNeeded
       //fsWatcher.Error   |> Observable.map errorToNeeded
    |] |> Observable.mergeArray

let handle (e: FileSystemEventArgs) =
    printfn "handle %A event '%s' '%s' " e.ChangeType e.Name e.FullPath 

let watch path filter throttleTime =
    // disposes watcher if observer subscription is disposed
    Observable.using (createWatcher path filter) createSources
    // filter out multiple equal events
    |> Observable.distinctUntilChanged
    // filter out multiple Changed
    |> Observable.throttle throttleTime
    |> Observable.subscribe handle

[<EntryPoint>]
let main _args =
    let path = @"C:\Temp\WatchDir"
    let filter = "*.zip"
    let throttleTime = TimeSpan.FromSeconds 10.
    use _subscription = watch path filter throttleTime
    System.Console.ReadKey() |> ignore
    0 // return an integer exit code

我可以通过添加一个函数来检查缓冲区数组中的重复项来做到这一点。

然后使用计时器在数组X时间内未被修改后执行该操作: -每次有东西写入缓冲区时重置计时器 —对tick执行动作

这还捕获了另一种复制类型。如果修改文件夹内的文件，该文件夹也会引发Change事件。

Function is_duplicate(str1 As String) As Boolean
    If lb_actions_list.Items.Count = 0 Then
        Return False
    Else
        Dim compStr As String = lb_actions_list.Items(lb_actions_list.Items.Count - 1).ToString
        compStr = compStr.Substring(compStr.IndexOf("-") + 1).Trim

        If compStr <> str1 AndAlso compStr.parentDir <> str1 & "\" Then
            Return False
        Else
            Return True
        End If
    End If
End Function

Public Module extentions
<Extension()>
Public Function parentDir(ByVal aString As String) As String
    Return aString.Substring(0, CInt(InStrRev(aString, "\", aString.Length - 1)))
End Function
End Module

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。

主要原因是 第一个事件的最后一次访问时间是当前时间(文件写入或更改时间)。 第二个事件是文件最初的最后一次访问时间。 我在代码下解决。

        var lastRead = DateTime.MinValue;

        Watcher = new FileSystemWatcher(...)
        {
            NotifyFilter = NotifyFilters.FileName | NotifyFilters.LastWrite,
            Filter = "*.dll",
            IncludeSubdirectories = false,
        };
        Watcher.Changed += (senderObject, ea) =>
        {
            var now = DateTime.Now;
            var lastWriteTime = File.GetLastWriteTime(ea.FullPath);

            if (now == lastWriteTime)
            {
                return;
            }

            if (lastWriteTime != lastRead)
            {
                // do something...
                lastRead = lastWriteTime;
            }
        };

        Watcher.EnableRaisingEvents = true;

一个可能的“黑客”是使用响应式扩展来限制事件，例如:

var watcher = new FileSystemWatcher("./");

Observable.FromEventPattern<FileSystemEventArgs>(watcher, "Changed")
            .Throttle(new TimeSpan(500000))
            .Subscribe(HandleChangeEvent);

watcher.EnableRaisingEvents = true;

在本例中，我将设置为50ms，在我的系统上这就足够了，但更高的值应该更安全。(就像我说的，这仍然是一个“hack”)。