FileSystemWatcher

I recently came across the interesting FileSystemWatcher class in the .NET Framework. It's pretty cool; the class will watch a folder, and raise events when there are changes to the files in that folder. You can specify a filter (like "*.txt") to only watch for certain files, and react when files are created, deleted, and modified.

It's pretty easy to come up with possible uses for this class. Maybe you have an old process somewhere that produces data files at irregular intervals; you could watch the output folder, and immediately act whenever one of those files is added. You could create a kind of auto-publishing system; let your users know that any file they save in a certain folder will automatically be posted for them. You could set up a mechanism for communicating between processes.

This last one is something that I've seen done before in VFP. A timer is set up to repeatedly check a certain location for a "message" file from another process, and then the app can react accordingly. A FileSystemWatcher makes this kind of setup simple - just set properties specifying the files to look for, and the file system events to watch.

Implementing this is straightforward as well. Create an instance of the class:

FileSystemWatcher fsw = new FileSystemWatcher();

Set its properties, and hook up an event handler:

fsw.Path = "C:\\SomeFolder\\WatchFolder\\";
fsw.Filter = "*.txt";
fsw.NotifyFilter = NotifyFilters.LastWrite;
fsw.Changed += new FileSystemEventHandler(this.OnFileChange);

Write the handler to do the work:

private void OnFileChange(object source, FileSystemEventArgs e)
{
// ...
}