FileSystemWatcher FileSystemWatcher FileSystemWatcher FileSystemWatcher Class

Definition

public ref class FileSystemWatcher : System::ComponentModel::Component, System::ComponentModel::ISupportInitialize

[System.IO.IODescription("")]
[System.IO.IODescription("FileSystemWatcherDesc")]
public class FileSystemWatcher : System.ComponentModel.Component, System.ComponentModel.ISupportInitialize

type FileSystemWatcher = class
    inherit Component
    interface ISupportInitialize

Public Class FileSystemWatcher
Inherits Component
Implements ISupportInitialize

Inheritance

ObjectObjectObjectObject

MarshalByRefObjectMarshalByRefObjectMarshalByRefObjectMarshalByRefObject

ComponentComponentComponentComponent

FileSystemWatcherFileSystemWatcherFileSystemWatcherFileSystemWatcher

Attributes

IODescriptionAttribute IODescriptionAttribute

Implements

ISupportInitializeISupportInitializeISupportInitializeISupportInitialize

Examples

The following example creates a FileSystemWatcher to watch the directory specified at run time. The component is set to watch for changes in LastWrite and LastAccess time, the creation, deletion, or renaming of text files in the directory. If a file is changed, created, or deleted, the path to the file prints to the console. When a file is renamed, the old and new paths print to the console.

#using <System.dll>

using namespace System;
using namespace System::IO;
using namespace System::Security::Permissions;

public ref class Watcher
{
private:
   // Define the event handlers.
   static void OnChanged( Object^ /*source*/, FileSystemEventArgs^ e )
   {
      // Specify what is done when a file is changed, created, or deleted.
      Console::WriteLine( "File: {0} {1}", e->FullPath, e->ChangeType );
   }

   static void OnRenamed( Object^ /*source*/, RenamedEventArgs^ e )
   {
      // Specify what is done when a file is renamed.
      Console::WriteLine( "File: {0} renamed to {1}", e->OldFullPath, e->FullPath );
   }

public:
   [PermissionSet(SecurityAction::Demand, Name="FullTrust")]
   int static run()
   {
      array<String^>^args = System::Environment::GetCommandLineArgs();

      // If a directory is not specified, exit program.
      if ( args->Length != 2 )
      {
         // Display the proper way to call the program.
         Console::WriteLine( "Usage: Watcher.exe (directory)" );
         return 0;
      }

      // Create a new FileSystemWatcher and set its properties.
      FileSystemWatcher^ watcher = gcnew FileSystemWatcher;
      watcher->Path = args[ 1 ];

      /* Watch for changes in LastAccess and LastWrite times, and 
          the renaming of files or directories. */
      watcher->NotifyFilter = static_cast<NotifyFilters>(NotifyFilters::LastAccess |
            NotifyFilters::LastWrite | NotifyFilters::FileName | NotifyFilters::DirectoryName);

      // Only watch text files.
      watcher->Filter = "*.txt";

      // Add event handlers.
      watcher->Changed += gcnew FileSystemEventHandler( Watcher::OnChanged );
      watcher->Created += gcnew FileSystemEventHandler( Watcher::OnChanged );
      watcher->Deleted += gcnew FileSystemEventHandler( Watcher::OnChanged );
      watcher->Renamed += gcnew RenamedEventHandler( Watcher::OnRenamed );

      // Begin watching.
      watcher->EnableRaisingEvents = true;

      // Wait for the user to quit the program.
      Console::WriteLine( "Press \'q\' to quit the sample." );
      while ( Console::Read() != 'q' );

      return 0;
   }
};

int main() {
   Watcher::run();
}

using System;
using System.IO;
using System.Security.Permissions;

public class Watcher
{
    public static void Main()
    {
        Run();
    }

    [PermissionSet(SecurityAction.Demand, Name = "FullTrust")]
    private static void Run()
    {
        string[] args = Environment.GetCommandLineArgs();

        // If a directory is not specified, exit program.
        if (args.Length != 2)
        {
            // Display the proper way to call the program.
            Console.WriteLine("Usage: Watcher.exe (directory)");
            return;
        }

        // Create a new FileSystemWatcher and set its properties.
        using (FileSystemWatcher watcher = new FileSystemWatcher())
        {
            watcher.Path = args[1];

            // Watch for changes in LastAccess and LastWrite times, and
            // the renaming of files or directories.
            watcher.NotifyFilter = NotifyFilters.LastAccess
                                 | NotifyFilters.LastWrite
                                 | NotifyFilters.FileName
                                 | NotifyFilters.DirectoryName;

            // Only watch text files.
            watcher.Filter = "*.txt";

            // Add event handlers.
            watcher.Changed += OnChanged;
            watcher.Created += OnChanged;
            watcher.Deleted += OnChanged;
            watcher.Renamed += OnRenamed;

            // Begin watching.
            watcher.EnableRaisingEvents = true;

            // Wait for the user to quit the program.
            Console.WriteLine("Press 'q' to quit the sample.");
            while (Console.Read() != 'q') ;
        }
    }

    // Define the event handlers.
    private static void OnChanged(object source, FileSystemEventArgs e) =>
        // Specify what is done when a file is changed, created, or deleted.
        Console.WriteLine($"File: {e.FullPath} {e.ChangeType}");

    private static void OnRenamed(object source, RenamedEventArgs e) =>
        // Specify what is done when a file is renamed.
        Console.WriteLine($"File: {e.OldFullPath} renamed to {e.FullPath}");
}

Imports System.IO
Imports System.Security.Permissions

Public Class Watcher

    Public Shared Sub Main()

        Run()

    End Sub

    <PermissionSet(SecurityAction.Demand, Name:="FullTrust")>
    Private Shared Sub Run()

        Dim args() As String = Environment.GetCommandLineArgs()

        ' If a directory is not specified, exit the program.
        If args.Length <> 2 Then
            ' Display the proper way to call the program.
            Console.WriteLine("Usage: Watcher.exe (directory)")
            Return
        End If

        ' Create a new FileSystemWatcher and set its properties.
        Using watcher As New FileSystemWatcher()
            watcher.Path = args(1)

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

            ' Only watch text files.
            watcher.Filter = "*.txt"

            ' Add event handlers.
            AddHandler watcher.Changed, AddressOf OnChanged
            AddHandler watcher.Created, AddressOf OnChanged
            AddHandler watcher.Deleted, AddressOf OnChanged
            AddHandler watcher.Renamed, AddressOf OnRenamed

            ' Begin watching.
            watcher.EnableRaisingEvents = True

            ' Wait for the user to quit the program.
            Console.WriteLine("Press 'q' to quit the sample.")
            While Chr(Console.Read()) <> "q"c
            End While
        End Using
    End Sub

    ' Define the event handlers.
    Private Shared Sub OnChanged(source As Object, e As FileSystemEventArgs)
        ' Specify what is done when a file is changed, created, or deleted.
        Console.WriteLine($"File: {e.FullPath} {e.ChangeType}")
    End Sub

    Private Shared Sub OnRenamed(source As Object, e As RenamedEventArgs)
        ' Specify what is done when a file is renamed.
        Console.WriteLine($"File: {e.OldFullPath} renamed to {e.FullPath}")
    End Sub

End Class

Remarks

Use FileSystemWatcher to watch for changes in a specified directory. You can watch for changes in files and subdirectories of the specified directory. You can create a component to watch files on a local computer, a network drive, or a remote computer.

To watch for changes in all files, set the Filter property to an empty string ("") or use wildcards ("*.*"). To watch a specific file, set the Filter property to the file name. For example, to watch for changes in the file MyDoc.txt, set the Filter property to "MyDoc.txt". You can also watch for changes in a certain type of file. For example, to watch for changes in text files, set the Filter property to "*.txt".

There are several types of changes you can watch for in a directory or file. For example, you can watch for changes in Attributes, the LastWrite date and time, or the Size of files or directories. This is done by setting the NotifyFilter property to one of the NotifyFilters values. For more information on the type of changes you can watch, see NotifyFilters.

You can watch for renaming, deletion, or creation of files or directories. For example, to watch for renaming of text files, set the Filter property to "*.txt" and call the WaitForChanged method with a Renamed specified for its parameter.

The Windows operating system notifies your component of file changes in a buffer created by the FileSystemWatcher. If there are many changes in a short time, the buffer can overflow. This causes the component to lose track of changes in the directory, and it will only provide blanket notification. Increasing the size of the buffer with the InternalBufferSize property is expensive, as it comes from non-paged memory that cannot be swapped out to disk, so keep the buffer as small yet large enough to not miss any file change events. To avoid a buffer overflow, use the NotifyFilter and IncludeSubdirectories properties so you can filter out unwanted change notifications.

For a list of initial property values for an instance of FileSystemWatcher, see the FileSystemWatcher constructor.

Please note the following when using the FileSystemWatcher class.

• Hidden files are not ignored.

• In some systems, FileSystemWatcher reports changes to files using the short 8.3 file name format. For example, a change to "LongFileName.LongExtension" could be reported as "LongFil~.Lon".

• This class contains a link demand and an inheritance demand at the class level that applies to all members. A SecurityException is thrown when either the immediate caller or the derived class does not have full-trust permission. For details about security demands, see Link Demands.

• The maximum size you can set for the InternalBufferSize property for monitoring a directory over the network is 64 KB.

Copying and moving folders

The operating system and FileSystemWatcher object interpret a cut-and-paste action or a move action as a rename action for a folder and its contents. If you cut and paste a folder with files into a folder being watched, the FileSystemWatcher object reports only the folder as new, but not its contents because they are essentially only renamed.

To be notified that the contents of folders have been moved or copied into a watched folder, provide OnChanged and OnRenamed event handler methods as suggested in the following table.

Events and Buffer Sizes

Note that several factors can affect which file system change events are raised, as described by the following:

• Common file system operations might raise more than one event. For example, when a file is moved from one directory to another, several OnChanged and some OnCreated and OnDeleted events might be raised. Moving a file is a complex operation that consists of multiple simple operations, therefore raising multiple events. Likewise, some applications (for example, antivirus software) might cause additional file system events that are detected by FileSystemWatcher.

• The FileSystemWatcher can watch disks as long as they are not switched or removed. The FileSystemWatcher does not raise events for CDs and DVDs, because time stamps and properties cannot change. Remote computers must have one of the required platforms installed for the component to function properly.

• If multiple FileSystemWatcher objects are watching the same UNC path in Windows XP prior to Service Pack 1, or Windows 2000 SP2 or earlier, then only one of the objects will raise an event. On machines running Windows XP SP1 and newer, Windows 2000 SP3 or newer or Windows Server 2003, all FileSystemWatcher objects will raise the appropriate events.

Note that a FileSystemWatcher may miss an event when the buffer size is exceeded. To avoid missing events, follow these guidelines:

• Increase the buffer size by setting the InternalBufferSize property.

• Avoid watching files with long file names, because a long file name contributes to filling up the buffer. Consider renaming these files using shorter names.

• Keep your event handling code as short as possible.

Constructors

Properties

Methods

Events

Security

SecurityPermission
for deriving from the ProcessStartInfo class. Demand value: InheritanceDemand; Named Permission Sets: FullTrust.

Applies to

See also

• NotifyFilter NotifyFilter NotifyFilter NotifyFilter
• NotifyFilters NotifyFilters NotifyFilters NotifyFilters
• FileSystemEventArgs FileSystemEventArgs FileSystemEventArgs FileSystemEventArgs
• FileSystemEventHandler FileSystemEventHandler FileSystemEventHandler FileSystemEventHandler
• Filter Filter Filter Filter
• IncludeSubdirectories IncludeSubdirectories IncludeSubdirectories IncludeSubdirectories
• InternalBufferOverflowException
• RenamedEventArgs RenamedEventArgs RenamedEventArgs RenamedEventArgs
• RenamedEventHandler RenamedEventHandler RenamedEventHandler RenamedEventHandler
• WaitForChangedResult WaitForChangedResult WaitForChangedResult WaitForChangedResult
• WatcherChangeTypes WatcherChangeTypes WatcherChangeTypes WatcherChangeTypes
• Using a FileSystemWatcher Component in a Windows Form