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Posted 21 Apr 2008


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Watching Folder Activity in C# .NET

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3.11 (19 votes)
2 Jul 2008     GPL3    
How to monitor a folder's activity with delegates and events threadsafe

Update 2008-07-03 - Vista Fix

If you are having trouble accessing the folder with permissions, you could always force UAC to elevate your securitygrade.


[PermissionSet(SecurityAction.Demand, Name = "FullTrust")] 

It's under System.Security.Permissions namespace.


I'm currently working on a project that needed to watch a folder's activity and trigger event in my application. So I started to search The Code Project and found out that the only code that existed was from 2003, and it did not even work (maybe because I'm on Vista?). Either ways, there were threads crossing other threads and fuzzy commenting, so I decided to clean it up. It's originally based on Jayesh Jaine's work who did this in VB.NET back in 2002. Then in 2003 Gerald Nelson picked it up, translated it to C#, but somehow he did not finish it. It was not threadsafe, blah blah blah...

Alright, let's continue.

Using the Code

It's really easy to use and I commented it well. As you can see below, we first declare _watchFolder as a FileSystemWatcher from the System.IO.

We just set the parameters to what we want to listen to and then connect the eventhandlers to some function.

// System.IO
        FileSystemWatcher _watchFolder = new FileSystemWatcher();

private void startActivityMonitoring(string sPath)
    // This is the path we want to monitor
    _watchFolder.Path = sPath;

    // Make sure you use the OR on each Filter because we need to monitor
    // all of those activities

    _watchFolder.NotifyFilter = System.IO.NotifyFilters.DirectoryName;

    _watchFolder.NotifyFilter = 
	_watchFolder.NotifyFilter | System.IO.NotifyFilters.FileName;
    _watchFolder.NotifyFilter = 
	_watchFolder.NotifyFilter | System.IO.NotifyFilters.Attributes;

    // Now hook the triggers(events) to our handler (eventRaised)
    _watchFolder.Changed += new FileSystemEventHandler(eventRaised);
    _watchFolder.Created += new FileSystemEventHandler(eventRaised);
    _watchFolder.Deleted += new FileSystemEventHandler(eventRaised);

    // Occurs when a file or directory is renamed in the specific path
    _watchFolder.Renamed += new System.IO.RenamedEventHandler(eventRenameRaised);

    // And at last.. We connect our EventHandles to the system API (that is all
    // wrapped up in System.IO)
        _watchFolder.EnableRaisingEvents = true;
    catch (ArgumentException)

Just a quick look at the function that handles the events.

/// <summary>
/// Triggered when an event is raised from the folder activity monitoring.
/// All types exists in System.IO
/// </summary>
/// <param name="sender"></param>
/// <param name="e">containing all data send from the event that got executed.</param>
private void eventRaised(object sender, System.IO.FileSystemEventArgs e)
    switch (e.ChangeType)
        case WatcherChangeTypes.Changed:
            TS_AddLogText(string.Format("File {0} has been modified\r\n", e.FullPath));

        case WatcherChangeTypes.Created:
            TS_AddLogText(string.Format("File {0} has been created\r\n", e.FullPath));

        case WatcherChangeTypes.Deleted:
            TS_AddLogText(string.Format("File {0} has been deleted\r\n", e.FullPath));

        default: // Another action

Points of Interest

One thing that I discovered while doing this is that when creating a file in the folder you are monitoring, windows is modifying this file twice.

Another thing is when an event is raised, the event is called from another thread. Now this causes it to crash if we don't make any control or component we want to access that was created on other threads to threadsafe. There is an example in the source code on how to do this.

Tip: Don't forget to set...

_watchFolder.EnableRaisingEvents = false;

... when you want it to stop listening. If you assign the listeners twice, it will trigger both events. Happy coding, my friends!


  • 21st April, 2008: First release
  • 3rd July, 2008: Vista fix


This article, along with any associated source code and files, is licensed under The GNU General Public License (GPLv3)


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Comments and Discussions

QuestionHelp about When files created, I wanna move them another directory Pin
cllunlu1-Dec-14 4:01
membercllunlu1-Dec-14 4:01 
GeneralMy vote of 5 Pin
rama charan15-Mar-12 22:13
memberrama charan15-Mar-12 22:13 
Questionhow to watching two folders? Pin
yuyejian12-Jun-10 22:10
memberyuyejian12-Jun-10 22:10 
GeneralThank you for this article Pin
TonyHenrique27-Mar-10 10:11
memberTonyHenrique27-Mar-10 10:11 
GeneralEmail the results Pin
Leigh Turner14-Apr-09 21:47
memberLeigh Turner14-Apr-09 21:47 
GeneralRe: Email the results Pin
MrMahjong15-Apr-09 1:46
memberMrMahjong15-Apr-09 1:46 
GeneralRe: Email the results Pin
Leigh Turner15-Apr-09 1:55
memberLeigh Turner15-Apr-09 1:55 
GeneralMy vote of 2 Pin
Gilad Kapelushnik29-Mar-09 22:05
memberGilad Kapelushnik29-Mar-09 22:05 
GeneralThe point. Pin
MrMahjong21-Apr-08 22:18
memberMrMahjong21-Apr-08 22:18 
QuestionWhat's the point? PinPopular
Shog921-Apr-08 13:13
sitebuilderShog921-Apr-08 13:13 

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