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)
{
// ...
}

Strangest Bug Ever

I recently came across an extremely odd bug in Visual Studio 2003, which I've since learned is known as the Haunted Keyboard bug. I was editing some code, and suddenly a few of my keys stopped responding. Pressing enter, tab, or the arrow keys did nothing, while the normal letter keys worked normally. Very strange. I actually physically checked the keyboard to see if something was jamming or sticking to the keys, before opening Notepad and verifying that they worked fine there.

The explanation is that this bug allows one of the docked Visual Studio windows, such as the Toolbox, to grab focus for command keystrokes, but not others. The interesting thing is that for different versions of VS there are different fixes - in one case you can simply select the Toolbox and then set focus back to the code editor, and in another you need to reset all settings. Also you may need to use a fixed-pitch font, for some reason. Interestingly I could not find any mention of this happening in VS2003, where I was getting it, but only in VS2005. There were also claims that this issue was resolved for the release version of VS2005, but also postings of users still experiencing it there.

In any case, I was glad to find that this was a known issue. It was one of the few times where I've wondered if I was literally hallucinating the behaviour I was seeing. I'm happy I wasn't, partly because I don't particularly want to hallucinate, and partly because Oh noes my enter key doesn't work! is a pretty lame hallucination, even for me :).