How do you monitor file changes in a directory using FileSystemWatcher?

Question

Utpal Vishwas · Answer

To monitor file changes in a directory in C#, use the built-in
FileSystemWatcher class from the System.IO namespace.
What FileSystemWatcher Can Track
It can detect changes such as:File creationFile modificationFile deletionFile 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} =andgt; {e.FullPath}");
    }
}
Notes
EnableRaisingEvents = true must be set to start monitoring.NotifyFilter helps filter what kind of changes you want to track.Filter = "*.txt" will limit monitoring to specific file types.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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How do you monitor file changes in a directory using FileSystemWatcher?

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What FileSystemWatcher Can Track

Basic Example: Monitor a Directory

Notes

Optional: Watch Subdirectories

Considerations

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