Monitor the file system with FileSystemWatcher in C# .NET Part 1

In this mini-series we’ll look at how you can use the FileSystemWatcher object to monitor the Windows file system for various changes.

A FileSystemWatcher object enables you to be notified when some change occurs in the selected part of the file system. This can be any directory, such as “c:\” or any subdirectory under the C: drive. So if you’d like to make sure you know if a change occurs on e.g. “c:\myfolder” – especially if it’s editable by your colleagues – then FileSystemWatcher is a good candidate.

Consider the following Console application:

class Program
{
	static void Main(string[] args)
	{
		RunFirstExample();
		Console.ReadKey();
	}

	private static void RunFirstExample()
	{
		FileSystemWatcher watcher = new FileSystemWatcher();
		watcher.Path = @"c:\mydirectory";
		watcher.Created += watcher_Created;
		watcher.Deleted += watcher_Deleted;
		watcher.EnableRaisingEvents = true;			
	}

	static void watcher_Deleted(object sender, FileSystemEventArgs e)
	{
		Console.WriteLine("File deleted. Name: {0}", e.Name);
	}

	static void watcher_Created(object sender, FileSystemEventArgs e)
	{
		Console.WriteLine("File created. Name: {0}", e.Name);
	}
}

In RunFirstExample we specify that we’re interested in monitoring the c:\mydirectory directory. Then we subscribe to the Created and Deleted events which represent the insertion of a new file and the deletion of an existing file in the directory. The FileSystemEventArgs has a couple of properties to show the event type, such as “Created” or “Deleted” in a WatcherChangeTypes enumeration, the file name and the file full path. We then start running the monitoring process by setting EnableRaisingEvents to true.

Note the call to Console.ReadKey(); in Main. The process won’t magically run in the background once Main is done. The FileSystemWatcher must sit within a continuous process, such as a Windows service.

Run the above code and insert a new file into the monitored directory. Then delete the file and watch the console output. Insertion example:

File creation monitored by filesystemwatcher

File deleted:

File deletion monitored by filesystemwatcher

Read the next part here.

Read all posts dedicated to file I/O here.

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About Andras Nemes
I'm a .NET/Java developer living and working in Stockholm, Sweden.

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