解决FileSystemWatcher事件多次触发的方法

作者: 江大鱼发表于 2008-07-23 21:55 原文链接阅读: 968 评论: 2

博客园已有几位同学发表了关于FileSystemWatcher事件多次触发的解决方法的文章，很好地解决了事件多次激发的问题。

主要方法有：

1.延迟激发法。

http://www.cnblogs.com/dragon/archive/2008/07/04/filesystemwatcher.html

原理是延迟调用事件的代理，将多次事件合并为一次,从而很好的解决了此问题，唯一的缺憾是时间激发不及时，不适用于实时性较高的系统。

2.临时禁用法。

void watcher_Changed(object sender, FileSystemEventArgs e) 2: {
if (watcher != null) 4: {
//解决执行两次的问题  6: watcher.EnableRaisingEvents = false; 7: Thread th = new Thread(new ThreadStart( 8: delegate() 9: {
Thread.Sleep(1000); 11: watcher.EnableRaisingEvents = true; 12: } 13: )); 14: th.Start(); 15: } 16: }

这种方法是监视单个文件的情况下的最简单解决办法。但是很明显，在监视多个文件的情况下就有很大的问题，文件的事件很可能丢失，在高并发的情况下很容易出问题。

我这里要提出的新的方法叫“检查最后更新时间法”，原理是在FileSystemWatcher事件激发时先检查更新的文件的最后更新时间是否已经被记录，如果未被记录则激发event，否则不激发。

具体代码如下

using System; 2: using System.Collections.Generic; 3: using System.Linq; 4: using System.Text; 5: using System.IO; 6:  7: namespace GiantSoft.Common 8: {
public class GiantFileSystemWatcher : IDisposable 10: {
private FileSystemWatcher m_Watcher; 12:  13: private Dictionary<string, DateTime> m_DictUpdateTime = new Dictionary<string, DateTime>(); 14:  15: public GiantFileSystemWatcher(string path, string filter) 16: {
m_Watcher = new FileSystemWatcher(path, filter); 18: m_Watcher.Error += new ErrorEventHandler(m_Watcher_Error); 19: m_Watcher.EnableRaisingEvents = false; 20: m_Watcher.IncludeSubdirectories = true; 21: } 22:  23: void m_Watcher_Error(object sender, ErrorEventArgs e) 24: {
LogUtil.LogError(e.GetException()); 26: } 27:  28: public bool Start() 29: {
if (m_FileChangeHandler != null) 31: {
m_Watcher.Changed += new FileSystemEventHandler(m_Watcher_Changed); 33: m_Watcher.Created += new FileSystemEventHandler(m_Watcher_Changed); 34: m_Watcher.Renamed += new RenamedEventHandler(m_Watcher_Changed); 35: m_Watcher.EnableRaisingEvents = true; 36: return true; 37: } 38: else 39: {
return false; 41: } 42: } 43:  44: void m_Watcher_Changed(object sender, FileSystemEventArgs e) 45: {
try 47: {
DateTime lastModifyTime = File.GetLastWriteTime(e.FullPath); 49: DateTime prevModifyTime = DateTime.MinValue; 50:  51: if (m_DictUpdateTime.TryGetValue(e.FullPath.ToLower(), out prevModifyTime)) 52: {
if (lastModifyTime <= prevModifyTime) 54: {
return; 56: } 57: else 58: {
m_DictUpdateTime[e.FullPath.ToLower()] = lastModifyTime; 60: } 61: } 62: else 63: {
m_DictUpdateTime[e.FullPath.ToLower()] = lastModifyTime; 65: } 66:  67: if (m_FileChangeHandler != null) 68: {
m_FileChangeHandler.Invoke(this, e); 70: } 71: } 72: catch (Exception exc) 73: {
LogUtil.LogError(exc); 75: } 76: } 77:  78: private FileSystemEventHandler m_FileChangeHandler; 79:  80: public event FileSystemEventHandler FileChangeHandler 81: {
add { m_FileChangeHandler += value; } 83: remove { m_FileChangeHandler -= value; } 84: } 85:  86: #region IDisposable Members 87:  88: public void Dispose() 89: {
m_DictUpdateTime.Clear(); 91: m_DictUpdateTime = null; 92: m_Watcher.EnableRaisingEvents = false; 93: if (m_FileChangeHandler != null) 94: {
m_Watcher.Changed -= new FileSystemEventHandler(m_Watcher_Changed); 96: m_Watcher.Created -= new FileSystemEventHandler(m_Watcher_Changed); 97: m_Watcher.Renamed -= new RenamedEventHandler(m_Watcher_Changed); 98: } 99: m_Watcher.Dispose(); 100: } 101:  102: #endregion 103: } 104: }