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Have you ever needed to monitor a specific directory or file for changes? .Net Framework has a class called FileSystemWatcher within System.IO namespace that allows developers to take action when a specific event occurs in the File System. In this posting, I’ll show you how you can use the FileSystemWatcher class to monitor your files or directories.

For our sample, let’s use the following hypothetical scenario: your company hosts its own website and for months, without success, you have been asking content editors not to store their image files within the folder reserved for web pages only. So, you decide to monitor the folder and take action if any violation happens.

How do you get this done using FileSystemWatcher? In the code sample below, you will notice that you just need to create an instance of FileSystemWatcher, add event handlers for the events you want to monitor, and tell your object to watch for events. It’s that simple!

In the implementation of the Created event handler above, I am just checking for extensions of image files explicitly. The FileSystemWatcher has a property called “Filter”, which allows you to define a mask of the type of files to watch (“*.jpg”, “doc*.*”, etc), but I couldn’t get more than one file extension associated with this property (if you know of another way, let me know).

So, still in the implementation sample, if an image file is created or copied into the monitored folder, an e-mail is fired to alert of the violation and the file is automatically deleted from the folder. Also, just to play nice and prevent any problems if the only copy of the file is deleted, the e-mail will also have a copy of the file attached to it. Another option would be to automatically move the file to the correct directory instead of just deleting it; however, if you take that approach, you’ll also have to check for crashes on the filename, at minimum.

Besides the Created event illustrated in our sample, you can also monitor the File System for the following events: Changed, Deleted, and Renamed. In our sample, we could also have implemented the Renamed event handler to prevent a user from bypassing the monitoring system by copying an image into the folder without an extension and renaming it later. And finally, if you are also looking for events in subdirectories, you can just set the FileSystemWatcher.IncludeSubdirectories property to true.

One thing to keep in mind is that, I have used a Console Application just to illustrate the implementation of the FileSystemWatcher class. However, if you decide to implement something similar that should run constantly, instead of a Console Application, you’ll probably want to look into creating a Windows Service and get your monitoring application running in the background.

Have Fun!

C# 3.0 and later versions give developers the ability to have underlying property structures automatically taken care by the compiler, which behind the scenes, creates the private members and implements the get and set inner workings. In this posting, I’ll cover how to create regular and automated properties in C#.

Before automated properties became available, the only way to create properties was to write code for each property we wanted to make available through our class. The snapshot below displays a Person class being consumed by the Program class. The Person class has three properties: FirstName, LastName, and DateOfBirth. In order to implement these properties in the correct encapsulated way, we needed three private members (declared at the top) that will only be accessible through the public properties.

Now, let’s see what changes when using automated properties. After modifying the Person class above to use automated properties, we have the following code:

The differences are clear. We basically replaced a regular block property declaration with a single line declaration by adding {get; set; } to the member declaration. The compiler will automatically create basic get and set blocks and the result will be transparent to other classes consuming your class. In addition to make it easier to create properties, we have also saved about 18 lines of code by switching just three properties to auto mode. Imagine not having to type several lines of code for classes requiring lots of properties.

You can also make one or more of your properties immutable by declaring the set accessor private. For instance, in our Person class, a Person might get married and need to change the Last Name, but the Date of Birth will never change. The code below displays how we can make DateOfBirth immutable using automated properties:

As we can see from the snapshot above, we just needed to declare the set accessor as private during the member declaration to prevent users from changing property values once the object has been created. The downside of this approach is that a constructor needs to be implemented in order to populate the immutable property at the time the class is instantiated.

Have Fun!

Wow! This is a feature I would like to have available on Excel, but until Microsoft wakes up, I’ll surely be giving Google Docs a try. Sometimes I have to create forms, in which some cells can only accept a certain type of data. When working on Excel to accomplish this goal, I usually can’t find a native way to validate the data without putting my VBA skills to work. (Note: as I’m not a heavy Excel user, let me know if I’m missing a feature already available in Excel).

Google has added a great feature to Google Spreadsheets, which allows users to determine which cells should match a specific data type. And there’s more; we can also decide whether invalid data will be automatically rejected or if just a warning will be given.

Here’s a quote from Google Blogoscoped about the new feature:

“For instance, you can select a column which is supposed to contain email addresses only. Now pick Tools -> Data Validation from the menu. You’ll be offered to restrict the cell content to only certain types of numbers, texts, or dates. Each type contains further restrictions; for instance, a text may be set so it must contain a certain string, or be an email, or be a valid URL.”

Thank you for this nice feature. Way to go Google!