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Have you ever wanted to write an application that constantly monitors a folder and raises events when there is any activity in that folder? In the good old days, using VB6 or an older version, you had to use Windows APIs to do something like this. It was not very simple and required lots of coding.
Microsoft .NET Framework has introduced classes such as System.IO and System.Diagnostics, which contain the FileSystemWatcher class that can raise events when a file is created/renamed/updated or deleted from the specified folder or any other activities.
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 the folder path|
Let's start coding this 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 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; for example, you can set the NotifyFilter property to Size if you want to monitor the changes in the file/folder size. Below is 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: Created, Changed, Deleted, Renamed, and Error. But because the Created, Changed, and Deleted events share the same event signature, we can write just one event handler. 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 that you will have to type the event declaration; 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
Now it's 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.
Use the FileSystemWatcher.Filter property to determine what files should be monitored. For example, setting the filter property to "*.txt" shall monitor all the files with extension txt. The default is *.*, which means all the files with extension are being monitored. If you want to monitor all the files, with and without extensions, 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 CDs. 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.
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, set it to false. The default is false.
The FileSystemWatcher.Path property supports Universal Naming Convention (UNC) paths. If the folder to which the path points is renamed, FileSystemWatcher reattaches itself to the new, renamed folder.
Hopefully, this article has shown you how simple it is to incorporate the FileSystemWatcher class in your application. Here are a few things that you could do with the FileSystemWatcher class:
- Import a file the moment it is copied/uploaded to a particular folder.
- Recreate a file if the file is deleted or something else is done to it.
- Notify all the applications depending upon a file the moment the file is renamed, deleted, or updated.
About the Author
Jayesh Jain works as a consultant 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. You can contact him on firstname.lastname@example.org.