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FileSystemEventHandler Delegate

Represents the method that will handle the Changed, Created, or Deleted event of a FileSystemWatcher class.

Namespace:  System.IO
Assembly:  System (in System.dll)

'Declaration
Public Delegate Sub FileSystemEventHandler ( _
	sender As Object, _
	e As FileSystemEventArgs _
)

Parameters

sender
Type: System.Object

The source of the event.

e
Type: System.IO.FileSystemEventArgs

The FileSystemEventArgs that contains the event data.

When you create a FileSystemEventHandler delegate, you identify the method that will handle the event. To associate the event with your event handler, add an instance of the delegate to the event. The event handler is called whenever the event occurs, unless you remove the delegate. For more information about event handler delegates, see Handling and Raising Events.

The following example shows how to create a FileSystemWatcher to monitor file changes (creates, deletes, renames, changes) occurring on a disk drive. The example also shows how to properly receive error notifications.

Imports System.IO

Module Module1
    Sub Main()
        ' Create a FileSystemWatcher to monitor all files on drive C. 
        Dim fsw As New FileSystemWatcher("C:\")

        ' Watch for changes in LastAccess and LastWrite times, and 
        ' the renaming of files or directories. 
        fsw.NotifyFilter = (NotifyFilters.LastAccess Or NotifyFilters.LastWrite _ 
            Or NotifyFilters.FileName Or NotifyFilters.DirectoryName)

        ' Register a handler that gets called when a  
        ' file is created, changed, or deleted. 
        AddHandler fsw.Changed, New FileSystemEventHandler(AddressOf OnChanged)

        ' The commented line of code below is a shorthand of the above line. 
        ' AddHandler fsw.Changed, AddressOf OnChanged 

        ' NOTE: The shorthand version is used in the remainder of this code. 
        ' FileSystemEventHandler 
        AddHandler fsw.Created, AddressOf OnChanged 
        ' FileSystemEventHandler 
        AddHandler fsw.Deleted, AddressOf OnChanged

        ' Register a handler that gets called when a file is renamed. 
        ' RenamedEventHandler 
        AddHandler fsw.Renamed, AddressOf OnRenamed

        ' Register a handler that gets called if the  
        ' FileSystemWatcher needs to report an error. 
        ' ErrorEventHandler 
        AddHandler fsw.Error, AddressOf OnError

        ' Begin watching.
        fsw.EnableRaisingEvents = True 

        ' Wait for the user to quit the program.
        Console.WriteLine("Press 'Enter' to quit the sample.")
        Console.ReadLine()
    End Sub 

    ' This method is called when a file is created, changed, or deleted. 
    Private Sub OnChanged(ByVal source As Object, ByVal e As FileSystemEventArgs)

        ' Show that a file has been created, changed, or deleted. 
        Dim wct As WatcherChangeTypes = e.ChangeType
        Console.WriteLine("File {0} {1}", e.FullPath, wct.ToString())
    End Sub 

    ' This method is called when a file is renamed. 
    Private Sub OnRenamed(ByVal source As Object, ByVal e As RenamedEventArgs)

        ' Show that a file has been renamed. 
        Dim wct As WatcherChangeTypes = e.ChangeType
        Console.WriteLine("File {0} {2} to {1}", e.OldFullPath, e.FullPath, wct.ToString())
    End Sub 

    ' This method is called when the FileSystemWatcher detects an error. 
    Private Sub OnError(ByVal source As Object, ByVal e As ErrorEventArgs)

        ' Show that an error has been detected.
        Console.WriteLine("The FileSystemWatcher has detected an error")

        ' Give more information if the error is due to an internal buffer overflow. 
        If TypeOf e.GetException Is InternalBufferOverflowException Then 
            ' This can happen if Windows is reporting many file system events quickly  
            ' and internal buffer of the  FileSystemWatcher is not large enough to handle this 
            ' rate of events. The InternalBufferOverflowException error informs the application 
            ' that some of the file system events are being lost.
            Console.WriteLine( _
                "The file system watcher experienced an internal buffer overflow: " _
                + e.GetException.Message)
        End If 
    End Sub 
End Module

.NET Framework

Supported in: 4.6, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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