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Home Forums How do you monitor file changes in a directory using FileSystemWatcher? – MindStick
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1 Answers

Utpal Vishwas
Utpal Vishwas 21 May 2025
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To monitor file changes in a directory in C#, use the built-in FileSystemWatcher class from the System.IO namespace.

What FileSystemWatcher Can Track

  1. It can detect changes such as:
  2. File creation
  3. File modification
  4. File deletion
  5. File renaming

Basic Example: Monitor a Directory

using System;
using System.IO;

class Program
{
    static void Main()
    {
        string pathToWatch = @"C:\MyWatchedFolder";

        using (FileSystemWatcher watcher = new FileSystemWatcher())
        {
            watcher.Path = pathToWatch;

            // Watch for changes in LastWrite and LastAccess time, and file name or directory name changes.
            watcher.NotifyFilter = NotifyFilters.LastWrite
                                 | NotifyFilters.FileName
                                 | NotifyFilters.DirectoryName;

            // Filter: watch all files
            watcher.Filter = "*.*";

            // Event handlers
            watcher.Changed += OnChanged;
            watcher.Created += OnChanged;
            watcher.Deleted += OnChanged;
            watcher.Renamed += OnRenamed;

            // Begin watching
            watcher.EnableRaisingEvents = true;

            Console.WriteLine($"Monitoring changes in: {pathToWatch}");
            Console.WriteLine("Press [Enter] to exit...");
            Console.ReadLine();
        }
    }

    private static void OnChanged(object source, FileSystemEventArgs e)
    {
        Console.WriteLine($"File {e.ChangeType}: {e.FullPath}");
    }

    private static void OnRenamed(object source, RenamedEventArgs e)
    {
        Console.WriteLine($"File Renamed: {e.OldFullPath} => {e.FullPath}");
    }
}

Notes

  1. EnableRaisingEvents = true must be set to start monitoring.
  2. NotifyFilter helps filter what kind of changes you want to track.
  3. Filter = "*.txt" will limit monitoring to specific file types.
  4. You can also watch subdirectories by setting IncludeSubdirectories = true.

Optional: Watch Subdirectories

watcher.IncludeSubdirectories = true;

Considerations

  • FileSystemWatcher may miss rapid successive changes (e.g., thousands of changes quickly).
  • You might want to debounce events using a timer or queue for performance in heavy-use cases.
  • On Linux/macOS (via .NET Core), it uses platform-specific mechanisms like inotify or FSEvents.
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