Monitor the file system with FileSystemWatcher in C# .NET Part 3: errors

In this and this post we looked at how to use FileSystemWatcher to monitor the creation, deletion and update of files within a directory. It can happen that there are more changes than the FileSystemWatcher object can handle. In that case FileSystemWatcher raises the Error event which you can subscribe to as follows:

static void Main(string[] args)
{
	RunErrorExample();
	Console.ReadKey();
}

private static void RunErrorExample()
{
	FileSystemWatcher watcher = new FileSystemWatcher();
	watcher.Path = @"c:\mydirectory";
	watcher.Error += watcher_Error;
	watcher.EnableRaisingEvents = true;
}

static void watcher_Error(object sender, ErrorEventArgs e)
{
	Exception ex = e.GetException();
	Console.WriteLine(ex.Message);
	if (ex.InnerException != null)
	{
		Console.WriteLine(ex.InnerException);
	}
}

Read the next and last installment on this topic here.

Read all posts dedicated to file I/O here.

Monitor the file system with FileSystemWatcher in C# .NET Part 2: updates

In this post we saw how to set up a FileSystemWatcher to monitor a directory for file insertions and creations.

The FileSystemWatcher object also lets you monitor a given directory for file updates. The following code is very similar to the one referred to in the above link. The difference is that we subscribe to the Renamed event:

static void Main(string[] args)
{
	RunUpdateExample();
	Console.ReadKey();
}

private static void RunUpdateExample()
{
	FileSystemWatcher watcher = new FileSystemWatcher();
	watcher.Path = @"c:\mydirectory";
	watcher.Renamed += watcher_Renamed;
	watcher.EnableRaisingEvents = true;
}

static void watcher_Renamed(object sender, RenamedEventArgs e)
{
	Console.WriteLine("File updated. Old name: {0}, new name: {1}", e.OldName, e.Name);
}

Again, we have the Console.ReadKey(); in Main to make sure that the console app doesn’t just quit, otherwise the file system watcher process dies.

If you run this code and rename a file in the monitored directory you may see an output similar to the following:

Read the next installment here.

Read all posts dedicated to file I/O here.

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 deleted:

Read the next part here.

Read all posts dedicated to file I/O here.