Have you 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 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 raise 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:
Control Name Control Type/Function txt_watchpath TextBox (for folder path) btn_startwatch Button (start watching) btn_stop Button (stop watching) txt_folderactivity Textbox (folder activity)
Coding
Let’s start coding the application. The 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 Filters we want to specify, making 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.
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 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
Coding
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 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 to 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.
Article first appeared at DevGuru.com
Jayesh Jain is working as applications consultant for a health company in Auckland, New Zealand. He has several years of n-Tier development experience and is currently working with Visual Basic.NET to develop interactive client solutions. He has a passion for Web development and in the spare time he likes to write articles. Contact him at: jainjayesh74@yahoo.com
