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Watching Folder Activity in VB.NET

, 13 Nov 2002
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In this article we're going to learn how to implement the FileSystemWatcher class using Microsoft Visual Basic .NET

Introduction

Ever wanted to write an application which constantly monitors a folder and raises events when there is any activity in that folder? In the good old days using VB6 or older you had to use the windows APIs to do something like this which was not very simple and required lots of coding.

The Microsoft .NET Framework has introduced classes like System.IO and System.Diagnostics, which contains the FileSystemWatcher class which can raises events when a file is created/renamed/updated or deleted from the specified folder or any other activities.

In this article we're going to learn how to implement the FileSystemWatcher class using Microsoft Visual Basic .NET. You will need the .NET framework installed, as well as Visual Studio .NET if you want to experiment with the source code presented in this article.

Getting Started

Open Visual Studio .NET and create a new Windows Application Project. Call it WatchFolder and click OK:

Create a user interface as shown in the image below. Add the following controls:

txt_watchpath           '      TextBox  (for folder path)
btn_startwatch          '      Button   (start watching)
btn_stop                '      Button   (stop watching)
txt_folderactivity      '      Textbox  (folder activity)
Lets start coding for this application, first thing we need to do is to import the required classes, type the following code before your class declaration
Imports System.IO
Imports System.Diagnostics
This shall import the necessary class required for our application we also need to declare a public variable for our FileSystemWatcher class
Public watchfolder As FileSystemWatcher
Also add the following code to the btn_start_click procedure.
watchfolder = New System.IO.FileSystemWatcher()

'this is the path we want to monitor
 watchfolder.Path = txt_watchpath.Text

'Add a list of Filter we want to specify
'make sure you use OR for each Filter as we need to
'all of those 

watchfolder.NotifyFilter = IO.NotifyFilters.DirectoryName
watchfolder.NotifyFilter = watchfolder.NotifyFilter Or _
                           IO.NotifyFilters.FileName
watchfolder.NotifyFilter = watchfolder.NotifyFilter Or _ 
                           IO.NotifyFilters.Attributes

' add the handler to each event
AddHandler watchfolder.Changed, AddressOf logchange
AddHandler watchfolder.Created, AddressOf logchange
AddHandler watchfolder.Deleted, AddressOf logchange

' add the rename handler as the signature is different
AddHandler watchfolder.Renamed, AddressOf logrename

'Set this property to true to start watching
watchfolder.EnableRaisingEvents = True

btn_startwatch.Enabled = False 
btn_stop.Enabled = True

'End of code for btn_start_click
The NotifyFilter property is used to specify the type of changes you want to watch. You can combine the notify filters to watch for one or more than one type of changes, eg. set the NotifyFilter property to Size if you want to monitor the changes in the file/folder size. Below are the list of notify filters
Attributes       ' (The attributes of the file or folder)
CreationTime     ' (The time the file or folder was created)
DirectoryName    ' (The name of the directory)
FileName         ' (The name of the file)
LastAccess       ' (The date the file or folder was last opened)
LastWrite        ' (The date the file or folder last had anything written to it)
Security         ' (The security settings of the file or folder)
Size             ' (The size of the file or folder)
The default is the bitwise OR combination of LastWrite, FileName, and DirectoryName.

The FileSystemWatcher class raises five events, which are Created, Changed, Deleted, Renamed and Error, but because Created, Changed, and Deleted events share the same event signature we can write just one event handler and we shall write one event handler for Renamed, because their event signatures are different.

Let's type code for handling the Created, Changed, and Deleted events raised by the FileSystemWatcher class. (Please note you will have to type the event declaration, as this procedure is not generated automatically)

Private Sub logchange(ByVal source As Object, ByVal e As _
                        System.IO.FileSystemEventArgs)
 If e.ChangeType = IO.WatcherChangeTypes.Changed Then
     txt_folderactivity.Text &= "File " & e.FullPath & _
                             " has been modified" & vbCrLf
 End If
 If e.ChangeType = IO.WatcherChangeTypes.Created Then
     txt_folderactivity.Text &= "File " & e.FullPath & _
                              " has been created" & vbCrLf
 End If
 If e.ChangeType = IO.WatcherChangeTypes.Deleted Then
     txt_folderactivity.Text &= "File " & e.FullPath & _
                             " has been deleted" & vbCrLf
 End If
End Sub
This is the code for handling the Renamed event raised by the FileSystemWatcher class.
Public Sub logrename(ByVal source As Object, ByVal e As _
                            System.IO.RenamedEventArgs)
   txt_folderactivity.Text &= "File" & e.OldName & _
                 " has been renamed to " & e.Name & vbCrLf
End Sub
And lastly this is the code for the btn_stop_click, which shall stop the monitor.
' Stop watching the folder
watchfolder.EnableRaisingEvents = False
btn_startwatch.Enabled = True
btn_stop.Enabled = False

Finally

Now it's the time to run the application and see it in action, please build and run the application, type the folder you want to monitor in the text box and click start watching to start watching that folder.

In the folder you specified, create a file, rename it, update it and delete it to see our application recording those changes.

More Information

Use FileSystemWatcher.Filter Property to determine what files should be monitored, eg setting filter property to "*.txt" shall monitor all the files with extension txt, the default is *.* which means all the files with extension, if you want to monitor all the files with and without extension please set the Filter property to "".
FileSystemWatcher can be used watch files on a local computer, a network drive, or a remote computer but it does not raise events for CD. It only works on Windows 2000 and Windows NT 4.0, common file system operations might raise more than one event. For example, when a file is edited or moved, more than one event might be raised. Likewise, some anti virus or other monitoring applications can cause additional events.

The FileSystemWatcher will not watch the specified folder until the path property has been set and EnableRaisingEvents is set to true. Set the FileSystemWatcher.IncludeSubdirectories Property to true if you want to monitor subdirectories; otherwise, false. The default is false.
FileSystemWatcher.Path property supports Universal Naming Convention (UNC) paths. If the folder, which the path points is renamed the FileSystemWatcher reattaches itself to the new renamed folder.

Conclusion

Hopefully this article has shown you how simple it is to incorporate the FileSystemWatcher class in your application. Here are few things that you could do with FileSystemWatcher class

  • Import a file the moment it is copied/uploaded to a particular folder
  • Recreate a file if the file is deleted or do something else.
  • Notify all the applications depending upon a file the moment the file is renamed, deleted or updated.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Jayesh Jain
Business Analyst
New Zealand New Zealand
Working as a Business Analyst for a leading software development organization in New Zealand. I have several years of n-Tier software development experience, about 10+ years in health sector and more than a year in graphics art industry. I am interested in Business improvement process, documentation and knowledge retaining strategies.

Comments and Discussions

 
QuestionCross-thread operation not valid: Control 'TextBox2' accessed from a thread other than the thread it was created on. Pinmembersuganthib22-Jul-14 5:05 
GeneralALOT of files really fast crashes the project ! Pinmembermavamaarten_youtube24-Apr-10 6:59 
AnswerRe: ALOT of files really fast crashes the project ! PinmemberMember 989452222-Jun-14 19:12 
GeneralFilesystemWatcher Pinmembersan0101806-Oct-08 6:56 
GeneralRe: FilesystemWatcher Pinmemberrootjumper19-Oct-09 2:42 
GeneralRe: FilesystemWatcher from Atul patel Pinmemberafr123ert564r817-Aug-11 0:23 
GeneralError: Cross-thread operation not valid PinmemberSiddiq-ur-Rahman Khurram6-Aug-08 2:00 
GeneralRe: Error: Cross-thread operation not valid Pinmemberr_mohd6-Aug-08 22:30 
GeneralRe: Error: Cross-thread operation Pinmemberafr123ert564r817-Aug-11 0:25 
reply from Atul Patel
 
add this line at sub or function starting .
 
Control.CheckForIllegalCrossThreadCalls = False
GeneralRe: Error: Cross-thread operation PinmemberMember 989452222-Jun-14 19:17 
GeneralMicrosoft example Pinmemberkelvin19972-Aug-08 4:42 
QuestionCopy Directory Pinmembermuhamad imran30-Jun-08 1:24 
AnswerRe: Copy Directory Pinmemberr_mohd6-Aug-08 22:26 
AnswerRe: Copy Directory Pinmemberchaos015327-Jul-12 22:19 
General"created" event fires.. followed by delete, another create, and two rename events Pinmembervegeta4ss20-Mar-08 4:52 
GeneralRe: "created" event fires.. followed by delete, another create, and two rename events Pinmembervegeta4ss20-Mar-08 7:07 
Questionhow about monitoring network storage? Pinmembermpmalajos19-Sep-07 21:33 
QuestionDoes FilesystemWatcher use DDE anyhow??? Pinmembersonumutneja13-Sep-07 19:53 
Generaldirectories and sub direectories PinmemberGC9N6-Jun-07 22:38 
GeneralFile creator Pinmemberletmetanka16-May-07 1:20 
QuestionCross Thread issues PinmemberHD-P27-Apr-07 8:56 
AnswerRe: Cross Thread issues PinmemberSchadenfroh28-May-07 6:02 
GeneralRe: Cross Thread issues Pinmemberibless12-Nov-07 8:48 
GeneralRe: Cross Thread issues Pinmemberibless12-Nov-07 8:52 
GeneralRe: Cross Thread issues Pinmemberrgkamble12-Aug-08 21:14 

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