Watch for File System Changes

Problem : You want your application to be notified when changes occur in the file system, such as when files are created or modified.

Solution: Many file systems provide ways for the operating system to notify programs when files and directories change. .NET provides the System.IO.FileSystemWatcher class to listen to these events.

class Program
{
    static void Main(string[] args)
    {
        if (args.Length < 1)
        {
            Console.WriteLine("Usage: WatchForChanges [FolderToWatch]");
            return;
        }

        System.IO.FileSystemWatcher watcher =
          new System.IO.FileSystemWatcher();
        watcher.Path = args[0];
        watcher.NotifyFilter = System.IO.NotifyFilters.Size |
            System.IO.NotifyFilters.FileName |
            System.IO.NotifyFilters.DirectoryName |
            System.IO.NotifyFilters.CreationTime;
        watcher.Filter = "*.*";
        watcher.Changed += watcher_Change;
        watcher.Created += watcher_Change;
        watcher.Deleted += watcher_Change;
        watcher.Renamed +=
          new System.IO.RenamedEventHandler(watcher_Renamed);

        Console.WriteLine(
         "Manipulate files in {0} to see activity...", args[0]);

        watcher.EnableRaisingEvents = true;

        while (true) { Thread.Sleep(1000); }
    }

    static void watcher_Change(object sender,
                               System.IO.FileSystemEventArgs e)
    {
        Console.WriteLine("{0} changed ({1})", e.Name, e.ChangeType);
    }

    static void watcher_Renamed(object sender,
                                System.IO.RenamedEventArgs e)
    {
        Console.WriteLine("{0} renamed to {1}", e.OldName, e.Name);
    }
}

					    

Here’s some sample output (during a create, rename, and delete of the file temp.txt):

D:\code\ch11\WatchForChanges\bin\Debug>WatchForChanges.exe d:\
Manipulate files in d:\ to see activity...
temp.txt changed (Created)
temp.txt changed (Changed)
temp.txt renamed to temp.rename
temp.rename changed (Deleted)

You can also call watcher.WaitForChange(), which will wait until something happens before returning, but usually the event-based mechanism will work for you.