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Working with the FileSystemWatcher in .NET

by Hannes DuPreez
Working with the FileSystemWatcher in .NET

FileSystemWatcher is a powerful tool you can employ in your .NET programming. Learn about it here. Examples are in C# and VB.NET.

Welcome to my article. Today, I would like to talk about using the FileSystemWatcher in .NET.

What Is FileSystemWatcher?

As the name implies, it watches the system for files. To put it better: It watches a folder for any changes. These changes could be things like file deletion, file renaming, changing the properties of a file, and so on.

Let's do a small practical example!

Open Visual Studio 2019 and create either a new C# or VB.NET Windows Forms application. Once your form has loaded, design it to resemble Figure 1.

It contains the following controls:

  • A large ListBox
  • Two textboxes with their Text properties set
  • Seven CheckBoxes

Name them anything you like, but keep in mind that my names may differ from yours.

Design
Figure 1: Design

Code

Add the following namespaces to your code.

C#

using System.IO;

VB.NET

Imports System.IO

Create the FileSystemWatcher object.

C#

   private FileSystemWatcher fsWatch;

VB.NET

   Private fsWatch As FileSystemWatcher

Set the properties for the FileSystemWatcher.

C#

   public Form1()
   {
      InitializeComponent();

      fsWatch = new FileSystemWatcher();
      fsWatch.SynchronizingObject = this;

      fsWatch.Changed += new FileSystemEventHandler(LogFile);
      fsWatch.Created += new FileSystemEventHandler(LogFile);
      fsWatch.Deleted += new FileSystemEventHandler(LogFile);
      fsWatch.Renamed += new RenamedEventHandler(LogRename);

   }

VB.NET

   Public Sub New()

      InitializeComponent()

      fsWatch = New FileSystemWatcher()
      fsWatch.SynchronizingObject = Me

      AddHandler fsWatch.Changed, New
         FileSystemEventHandler(AddressOf LogFile)
      AddHandler fsWatch.Created, New
         FileSystemEventHandler(AddressOf LogFile)
      AddHandler fsWatch.Deleted, New
         FileSystemEventHandler(AddressOf LogFile)
      AddHandler fsWatch.Renamed, New
         RenamedEventHandler(AddressOf LogRename)

   End Sub

Here, you set the SynchronizingObject to the current form. This allows the watcher to keep watching while the form is open. You then create four event handlers for each possible file change. Let's add them now.

C#

   void LogRename(object sender, RenamedEventArgs e)
   {

      lstLog.Items.Add(string.Format("{0:G} | {1} |
         Renamed from {2}", DateTime.Now, e.FullPath, e.OldName))

   }

   void LogFile(object sender, FileSystemEventArgs e)
   {

      lstLog.Items.Add(string.Format("{0:G} | {1} | {2}",
         DateTime.Now, e.FullPath, e.ChangeType));

   }

VB.NET

   Private Sub LogRename(ByVal sender As Object, ByVal e As _
         RenamedEventArgs)

      lstLog.Items.Add(String.Format("{0:G} | {1} | _
         Renamed from {2}", DateTime.Now, e.FullPath, e.OldName))

   End Sub

   Private Sub LogFile(ByVal sender As Object, ByVal e _
         As FileSystemEventArgs)

      lstLog.Items.Add(String.Format("{0:G} | {1} | {2}", _
         DateTime.Now, e.FullPath, e.ChangeType))

   End Sub

When a file's properties changes or gets renamed or moved, these events will fire. All they do is to simply log the current date and time along with the old and new names (if renamed), and the specific changed that has occurred.

Now, let's add the final event to control which properties we'd like to track.

C#

   private void chkMonitor_CheckedChanged(object sender,
      EventArgs e)
   {

      string strFolder = txtFolder.Text;
      bool blnExists = Directory.Exists(strFolder);

      if (blnExists)
      {

         fsWatch.Path = strFolder;
         fsWatch.Filter = FileFilterInput.Text;
         fsWatch.IncludeSubdirectories = chkSubFolders.Checked;


         NotifyFilters notificationFilters = new NotifyFilters();
         if (chkAttributes.Checked) notificationFilters =
            notificationFilters | NotifyFilters.Attributes;
         if (chkCreationTime.Checked) notificationFilters =
            notificationFilters | NotifyFilters.CreationTime;
         if (chkFileName.Checked) notificationFilters =
            notificationFilters | NotifyFilters.FileName;
         if (chkLastWrite.Checked) notificationFilters =
            notificationFilters | NotifyFilters.LastWrite;
         if (chkSize.Checked) notificationFilters =
            notificationFilters | NotifyFilters.Size;
         fsWatch.NotifyFilter = notificationFilters;

         fsWatch.EnableRaisingEvents = chkMonitor.Checked;

      }
      else if (chkMonitor.Checked)
      {

         MessageBox.Show("Invalid Folder.", "Invalid Folder",
            MessageBoxButtons.OK, MessageBoxIcon.Error);
         chkMonitor.Checked = false;

      }

   }

VB.NET

   Private Sub chkMonitor_CheckedChanged(ByVal sender As Object, _
         ByVal e As EventArgs) Handles chkMonitor.CheckedChanged

      Dim strFolder As String = txtFolder.Text
      Dim blnExists As Boolean = Directory.Exists(strFolder)

      If blnExists Then

         fsWatch.Path = strFolder
         fsWatch.Filter = FileFilterInput.Text
         fsWatch.IncludeSubdirectories = chkSubFolders.Checked
         Dim notificationFilters As NotifyFilters = New _
            NotifyFilters()
         If chkAttributes.Checked Then notificationFilters = _
            notificationFilters Or NotifyFilters.Attributes
         If chkCreationTime.Checked Then notificationFilters = _
            notificationFilters Or NotifyFilters.CreationTime
         If chkFileName.Checked Then notificationFilters = _
            notificationFilters Or NotifyFilters.FileName
         If chkLastWrite.Checked Then notificationFilters = _
            notificationFilters Or NotifyFilters.LastWrite
         If chkSize.Checked Then notificationFilters = _
            notificationFilters Or NotifyFilters.Size
         fsWatch.NotifyFilter = notificationFilters
         fsWatch.EnableRaisingEvents = chkMonitor.Checked

      ElseIf chkMonitor.Checked Then

         MessageBox.Show("Invalid Folder.", "Invalid Folder", _
            MessageBoxButtons.OK, MessageBoxIcon.[Error])
         chkMonitor.Checked = False

      End If

   End Sub

Here, we set the various properties we'd like to interrogate.

Conclusion

As you can see, the FilesystemWatcher is quite useful and versatile. Have a play around with it and see how you can track other folder and file changes within your system.

This article was originally published on Wednesday Jan 22nd 2020
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