为什么FileSystemWatcher会触发两次 [英] Why does FileSystemWatcher fire twice

问题描述

为什么FileSystemWatcher会触发两次?有一种简单的方法可以修复它吗?当然，如果我更新或编辑文本文件，它应该只触发一次?

why does the FileSystemWatcher fire twice? Is there an easy way to fix it? Surely if I update or edit the text file it should only fire once?

此处的链接 http://weblogs.asp. net/ashben/archive/2003/10/14/31773.aspx 说

1. 事件被引发两次-如果事件处理程序(AddHander FSW.Created，AddressOf FSW_Created)为 明确指定.这是因为默认情况下，公共事件 自动调用相应的受保护方法(OnChanged， OnCreated，OnDeleted，OnRenamed).要解决此问题，只需 删除显式事件处理程序(AddHandler ...).

1. Events being raised twice - An event will be raised twice if an event handler (AddHander FSW.Created, AddressOf FSW_Created) is explicitly specified. This is because, by default, the public events automatically call the respective protected methods (OnChanged, OnCreated, OnDeleted, OnRenamed). To correct this problem, simply remove the explicit event handler (AddHandler ...).

删除显式事件处理程序"是什么意思?

What does "remove the explicit event handler" mean?

Imports System.IO

Public Class Form2

    Private Sub FileSystemWatcher1_Changed(ByVal sender As System.Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed

        'this fires twice
        MessageBox.Show("test")

    End Sub

    Private Sub Form2_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        FileSystemWatcher1.Path = "C:\Users\c\Desktop\test\"
        FileSystemWatcher1.NotifyFilter = NotifyFilters.LastAccess Or NotifyFilters.LastWrite Or NotifyFilters.FileName Or NotifyFilters.DirectoryName Or NotifyFilters.CreationTime

        FileSystemWatcher1.IncludeSubdirectories = False
        FileSystemWatcher1.Filter = "text.txt"

    End Sub

End Class

推荐答案

更新:

我想出了两种解决方案.一个使用线程，另一个不使用.选择:-).

I have come up with 2 solutions. One uses Threads, and the other doesn't. Take your pick :-).

无线程:

Imports System.IO

Public Class Form1
    Private Sub FileSystemWatcher1_Changed(ByVal sender As System.Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed
        Dim watcher As System.IO.FileSystemWatcher = sender
        watcher.EnableRaisingEvents = False

        'Do work here while new events are not being raised.
        MessageBox.Show("Test")

        watcher.EnableRaisingEvents = True 'Now we can begin watching for new events.

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        FileSystemWatcher1.Path = "C:\Users\c\Desktop\test"
        FileSystemWatcher1.NotifyFilter = NotifyFilters.LastWrite
        FileSystemWatcher1.IncludeSubdirectories = False
        FileSystemWatcher1.Filter = "test.txt"


    End Sub

    Private Sub FileSystemWatcher_OnChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)

    End Sub

End Class

此解决方案(无线程)将watcher.EnableRaisingEvents设置为False.在此之后，您通常将处理任何受影响(或更改)的文件.完成工作后，它将EnableRaisingEvents设置回True.

This solution (without threading), sets the watcher.EnableRaisingEvents to False. It is after this point where you would normally process whatever files are affected (or changed). It then sets the EnableRaisingEvents back to True after your work is done.

带有线程:

Imports System.IO

Public Class Form1
    Private Sub FileSystemWatcher1_Changed(ByVal sender As System.Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed
        FileSystemWatcher1.EnableRaisingEvents = False
        Threading.Thread.Sleep(250)
        FileSystemWatcher1.EnableRaisingEvents = True


        MessageBox.Show("test")


    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        FileSystemWatcher1.Path = "C:\Users\c\Desktop\test"
        FileSystemWatcher1.NotifyFilter = NotifyFilters.LastWrite
        FileSystemWatcher1.IncludeSubdirectories = False
        FileSystemWatcher1.Filter = "test.txt"


    End Sub

    Private Sub FileSystemWatcher_OnChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)

    End Sub

End Class

此解决方案虽然有点 hacky ，但确实有效.基于您不需要每250ms检查一次更改的假设，它会禁用250ms的新更改/事件检查，然后重新启用检查.我已经尝试了几乎所有我能想到的一切，为您找到了一个真正的解决方案，但这将在此期间起作用.

This solution, although a bit hacky, does work. It disables checking for new changes/events for 250ms and then re-enables checking, based on the assumption that you won't been needing to check for a change every 250ms. I have tried almost everything that I could think of to get a real solution for you but this will work in the meantime.

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