Is there some mechanism by which I can be notified (in C#) when a file is modified on the disc?
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2See this [answer](http://stackoverflow.com/questions/381976/handling-multiple-change-events-in-filesystemwatcher/382996#382996) for more information on the FileSystemWatcher class and the events it raises. – ChrisF Apr 21 '12 at 13:02
3 Answers
240
You can use the FileSystemWatcher class.
public void CreateFileWatcher(string path)
{
// Create a new FileSystemWatcher and set its properties.
FileSystemWatcher watcher = new FileSystemWatcher();
watcher.Path = path;
/* Watch for changes in LastAccess and LastWrite times, and
the renaming of files or directories. */
watcher.NotifyFilter = NotifyFilters.LastAccess | NotifyFilters.LastWrite
| NotifyFilters.FileName | NotifyFilters.DirectoryName;
// Only watch text files.
watcher.Filter = "*.txt";
// Add event handlers.
watcher.Changed += new FileSystemEventHandler(OnChanged);
watcher.Created += new FileSystemEventHandler(OnChanged);
watcher.Deleted += new FileSystemEventHandler(OnChanged);
watcher.Renamed += new RenamedEventHandler(OnRenamed);
// Begin watching.
watcher.EnableRaisingEvents = true;
}
// Define the event handlers.
private static void OnChanged(object source, FileSystemEventArgs e)
{
// Specify what is done when a file is changed, created, or deleted.
Console.WriteLine("File: " + e.FullPath + " " + e.ChangeType);
}
private static void OnRenamed(object source, RenamedEventArgs e)
{
// Specify what is done when a file is renamed.
Console.WriteLine("File: {0} renamed to {1}", e.OldFullPath, e.FullPath);
}
Dirk Vollmar
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14Thanks for the nice example. I'll also point out that you can use the method WaitForChanged on FileSystemWatcher if you are looking for a blocking (synchronous) way to watch for changes. – Mark Meuer Sep 20 '13 at 17:38
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23Thanks for this example. The MSDN has pretty much the same [here](http://msdn.microsoft.com/en-us/library/system.io.filesystemwatcher.filter%28v=vs.100%29.aspx). Also, some people might want to watch a whole directory tree - use `watcher.IncludeSubdirectories = true;` to achieve that. – Oliver Nov 14 '13 at 22:59
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1`OnChange` fires without actual change (_e.g: hitting `ctrl+s` without any actual change_), is there any way to detect fake changes? – Mehdi Dehghani Oct 26 '19 at 09:14
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1@MehdiDehghani: Not that I know of, the only way seems to be to actually keep a snapshot of the file and compare that byte-wise to the current (presumably changed) version. The `FileSystemWatcher` only is able to detect events at the file system level (i.e. if the OS triggers an event). In your case Ctrl+S triggers such an event (whether that happens or not depends on the actual application though). – Dirk Vollmar Oct 26 '19 at 09:16
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Doesn't work in my case. I've got Valve's Steam changing appmanifest_appid.acf in the steamapps folder, and I'd like to get notified when the application updates. The file updates when the game starts to update, notepad++ detects the change and prompts to reload the file. But the `FileSystemWatcher` doesn't detect these changes. I coded it correctly, because I do get notified when I edit the manifest file in the notepad++ and press Ctrl+S. – KulaGGin Jun 21 '22 at 20:48
75
That would be System.IO.FileSystemWatcher.
Mihai Limbășan
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The doc said using System.IO only https://learn.microsoft.com/en-us/dotnet/api/system.io.filesystemwatcher?view=net-7.0 – Ray Chakrit Dec 31 '22 at 13:40
