Keep an eye on file system changes with VB.NET's FileSystemWatcher

FileSystemWatcher is a component in Visual Studio .NET that allows you to respond to file system changes. It's very handy whenever you need to perform a certain action in response to a file being updated and in numerous other situations.

Using FileSystemWatcher in your app

In order to add FileSystemWatcher to your Windows application, click on a Toolbox and find FileSystemWatcher under the list's Components section. Double-click FileSystemWatcher, and then the component will be visible under the Windows form (by default, it will be FileSystemWatcher1).

Now you are ready to set the properties of FileSystemWatcher1. This is how I set the following properties of the control through the Properties window in our example:

|> Filter: abc.txt
|> NotifyFilter: LastAccess
|> Path: C:\temp

Then I double-click FileSystemWatcher1 and add the following code to its Changed event:

        MessageBox.Show("file changed")

In order to get the example to work, you need to create a file in your c:/temp directory called abc.txt since the code assumes you already have this file. Then start your Windows application and -- while it's running -- open, edit, save, and close abc.txt. You should see the message box show up stating the file has changed. If you open the file but you don't save any changes to it, you will not see the message box since the NotifyFilter stated Write but not Open. In order to watch for changes in a particular directory, you would have to change the Filter property and the NotifyFilter property accordingly.