Question

为什么FileSystemWatcher会触发两次？有没有一种简单的方法来解决它？当然，如果我更新或编辑文本文件，它应该只触发一次？

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

两次引发的事件 - 如果事件处理程序（AddHander FSW.Created，AddressOf FSW_Created）是一个事件将被引发两次   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）。要简单地解决这个问题   删除显式事件处理程序（AddHandler ...）。

＆＃34;删除显式事件处理程序＆＃34;意思？

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

Answer 1

更新

我想出了两个解决方案。一个使用Threads，另一个不使用。请选择： - ）。

没有线程：

Imports System.IO

Public Class Form1
    Private Sub FileSystemWatcher1_Changed(ByVal sender As System.Object, ByVal e As System.IO.FileSystemEventArgs) Handles FileSystemWatcher1.Changed
        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，您通常会处理受影响（或更改）的任何文件。然后，在完成工作后，它会将EnableRaisingEvents设置为True。

使用线程：

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

这个解决方案虽然有点 hacky ，但确实有效。它会禁用检查250ms的新更改/事件，然后根据您不需要每250ms检查一次更改的假设重新启用检查。我已经尝试了几乎所有我能想到的东西来为你找到一个真正的解决方案，但这同时也适用。

Answer 2

检查e.ChangeType。我想你会得到两个不同的通知。也许是LastAccess和LastModified。在这种情况下，这是预期的行为。

Answer 3

今天我在FileSystemWatcher中崩溃并找到了这个网站。建议的Thread.Sleep不能完全消除问题。用快速反整数测试。并阻止UI。最有问题的是初创公司，它在5秒时跌幅低谷。然后我在TimerWatcherChanged.Tick中立即设置FileSystemWatcher1.EnableRaisingEvents = False并且再也没有启用...但令人惊讶的是，反击仍然可以赶上4个事件！我想与可调节的Timer共享我的解决方案，无阻塞。欢迎反馈。

Imports System.IO

Imports System.Diagnostics

Public Class Form1
  Dim fileName As String
  Dim Fsw_counter As Integer
  WithEvents TimerWatcherChanged As New Windows.Forms.Timer
  WithEvents TimerTest As New Windows.Forms.Timer

  Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
    TimerWatcherChanged.Interval = 100
    TimerTest.Interval = 100 : TimerTest.Start()
    TextBox1.Text = "C:\Downloads\New Text Document.txt"
    TextBox1.SelectionStart = TextBox1.Text.Length
    WatcherSetup()
  End Sub

  Sub WatcherSetup()
    fileName = TextBox1.Text
    FileSystemWatcher1.IncludeSubdirectories = False
    FileSystemWatcher1.Path = Path.GetDirectoryName(fileName)
    FileSystemWatcher1.Filter = Path.GetFileName(fileName)
    FileSystemWatcher1.NotifyFilter = NotifyFilters.LastWrite
    FileSystemWatcher1.EnableRaisingEvents = True
  End Sub

  Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
    WatcherSetup()
  End Sub

  Private Sub FileSystemWatcher1_Changed(sender As Object, e As FileSystemEventArgs) Handles FileSystemWatcher1.Changed
    If TimerWatcherChanged.Enabled = False Then
      TimerWatcherChanged.Enabled = True
      Fsw_counter += 1
      ' ***** Your WATCH Code put here... *****
    End If
  End Sub

  Private Sub TimerWatcherChanged_Tick(sender As Object, e As EventArgs) Handles TimerWatcherChanged.Tick
    TimerWatcherChanged.Enabled = False
  End Sub

  Private Sub TimerTest_Tick(ByVal sender As Object, ByVal e As System.EventArgs) Handles TimerTest.Tick
    TextBox2.Text = "Changed: " & Fsw_counter
    If TimerWatcherChanged.Enabled = True Then
      TextBox2.BackColor = Color.Red
    Else
      TextBox2.BackColor = Color.LawnGreen
    End If
  End Sub
End Class

为什么FileSystemWatcher会触发两次

3 个答案: