FileSystemWatcher事件多次触发的解决方法
转自:http://www.cnblogs.com/dragon/archive/2008/07/04/filesystemwatcher.html
1、问题描述
程序里需要监视某个目录下的文件变化情况: 一旦目录中出现新文件或者旧的文件被覆盖,程序需要读取文件内容并进行处理。于是使用了下面的代码:
public void Initial()
{
System.IO.FileSystemWatcher fsw = new System.IO.FileSystemWatcher();
fsw.Filter = "*.*";
fsw.NotifyFilter = NotifyFilters.FileName |
NotifyFilters.LastWrite |
NotifyFilters.CreationTime;
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// Add event handlers.
fsw.Created += new FileSystemEventHandler(fsw_Changed);
fsw.Changed += new FileSystemEventHandler(fsw_Changed);
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// Begin watching.
fsw.EnableRaisingEvents = true;
}
void fsw_Changed(object sender, FileSystemEventArgs e)
{
MessageBox.Show("Changed", e.Name);
}
结果发现当一个文件产生变化时,Change事件被反复触发了好几次。这样可能的结果是造成同一文件的重复处理。
2、解决方案:
在Google上进行一番搜索后,得到了下面的一段信息: <<http://www.cnblogs.com/RicCC/archive/2006/12/16/filesystem-watcher.html>>
"...可以参考log4net的做法。通过一个计时器,在文件事件处理中让计时器延迟一段时间之后,再执行加载新的配置文件操作。这样可以避免对文件做一次操作触发了多个更改事件,而多次加载配置文件。"
fsw.Filter = "*.*";
fsw.NotifyFilter = NotifyFilters.FileName |
NotifyFilters.LastWrite |
NotifyFilters.CreationTime;
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// Add event handlers.
fsw.Created += new FileSystemEventHandler(fsw_Changed);
fsw.Changed += new FileSystemEventHandler(fsw_Changed);
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// Begin watching.
fsw.EnableRaisingEvents = true;
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// Create the timer that will be used to deliver events. Set as disabled
if (m_timer == null)
{
//设置定时器的回调函数。此时定时器未启动
m_timer = new System.Threading.Timer(new TimerCallback(OnWatchedFileChange), null, Timeout.Infinite, Timeout.Infinite);
}
void fsw_Changed(object sender, FileSystemEventArgs e)
{
Mutex mutex = new Mutex(false, "FSW");
mutex.WaitOne();
if (!files.Contains(e.Name))
{
files.Add(e.Name);
}
mutex.ReleaseMutex();
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//重新设置定时器的触发间隔,并且仅仅触发一次
m_timer.Change(TimeoutMillis, Timeout.Infinite);
}
private void OnWatchedFileChange(object state)
{
List<String> backup = new List<string>();
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Mutex mutex = new Mutex(false, "FSW");
mutex.WaitOne();
backup.AddRange(files);
files.Clear();
mutex.ReleaseMutex();
foreach (string file in backup)
{
MessageBox.Show("File Change", file + " changed");
}
}
1、问题描述
程序里需要监视某个目录下的文件变化情况: 一旦目录中出现新文件或者旧的文件被覆盖,程序需要读取文件内容并进行处理。于是使用了下面的代码:
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2、解决方案:
在Google上进行一番搜索后,得到了下面的一段信息: <<http://www.cnblogs.com/RicCC/archive/2006/12/16/filesystem-watcher.html>>
"...可以参考log4net的做法。通过一个计时器,在文件事件处理中让计时器延迟一段时间之后,再执行加载新的配置文件操作。这样可以避免对文件做一次操作触发了多个更改事件,而多次加载配置文件。"
研究了log4net的代码 - XmlConfigurator.cs,然后参照log4net对代码作了如下改动:
基本思想是使用定时器,在事件触发时开始启动定时器,并记下文件名。当定时器到时,才真正对文件进行处理。
(1). 定义变量
private int TimeoutMillis = 2000; //定时器触发间隔
System.IO.FileSystemWatcher fsw = new System.IO.FileSystemWatcher();
System.Threading.Timer m_timer = null;
List<String> files = new List<string>(); //记录待处理文件的队列
(2). 初始化FileSystemWatcher和定时器System.IO.FileSystemWatcher fsw = new System.IO.FileSystemWatcher();
System.Threading.Timer m_timer = null;
List<String> files = new List<string>(); //记录待处理文件的队列
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(3). 文件监视事件触发代码:修改定时器,记录文件名待以后处理
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(4). 定时器事件触发代码:进行文件的实际处理
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完整的代码请下载示例程序。
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