The C# column

Using the FileSystemWatcher Component

In this article we will walk through the process of using the FileSystemWatcher component and watching the changes made to a subfolder/files of a selected folder.

The FileSystemWatcher component can keep track of creation, deletion, changing and renaming of a file/folder. It conveys to the application information about changes done to the file system by throwing events. It throws the Created, Deleted, Changed and Renamed events respectively. The name and path of the file/folder being changed is also made available in the event handlers.

The FileSystemWatcher component can watch files on a local computer, a network drive, or a remote computer. We can specify which files to watch by setting the appropriate value in the Filter property. If we wish to watch all the files we must set the Filter property to an empty string (“”). To watch a specific file, we must assign that filename to the Filter property. We can also use wildcards to specify certain type of file. For example, to watch for changes in EXE files, we can set the Filter property to “*.exe”.

The component has a property called NotifyFilter that can be used to specify the types of changes viz. changes in attribute, last write date and time, size, etc.

Having this much of knowledge about FileSystemWatcher component in hand, we can now use the component in our application.

We will create an application that uses the FileSystemWatcher control to keep watch on the folder selected by the user, an watch whether a file/folder is created, changed or deleted.

Create a WinForm application and put the controls on the form as shown in following figure.

We have added three list boxes to list the files/folders being created, changed or deleted. The ‘Watch Folder’ button allows the user to select a folder to watch. The path of the selected folder gets displayed on the label placed next to the ‘Watch Folder’ button. The ‘Clear’ button allows the user to delete the items listed in the list box having input focus.

In addition to these controls, add the FolderBrowserDialog control from the ‘Windows Forms’ tab and FileSystemWatcher component from the ‘Components’ tab of the ToolBox. The controls, their names and event handlers are given in the following table.

Add handlers for the Created, Deleted and Changed events. Also Set the IncludeSubdirectories property of the FileSystemWatcher component to true.

When the application is run, the user has to first select a folder to watch. He can do so by clicking the ‘Watch Folder’ button. We have displayed the ‘Browse For Folder’ standard dialog box in which user can select the folder. The dialog is displayed by calling the ShowDialog( ) method as shown below.

private void butwatch_Click ( object sender, System.EventArgs e )
{
  if ( browser.ShowDialog( ) == DialogResult.OK )
   {
      watcher.Path =  browser.SelectedPath ;
      label1.Text = browser.SelectedPath ;
   }
}

We have specified the folder to watch by setting the Path property of the FileSystemWatcher class to the path of selected folder. The path of selected folder is retrieved from the SelectedPath property of the FolderBrowserDialog class. We have displayed the path on the label.

The handlers added for the FileSystemWatcher events are given below.

private void watcher_Changed ( object sender, System.IO.FileSystemEventArgs e )
{
   listchange.Items.Add ( e.FullPath ) ;
}
   private void watcher_Created ( object sender,
   System.IO.FileSystemEventArgs e )
   {
      listcreate.Items.Add ( e.FullPath ) ;
   }
   private void watcher_Deleted ( object sender,
   System.IO.FileSystemEventArgs e )
   {
      listdelete.Items.Add ( e.FullPath ) ;
   }

In these handlers we have only added the full path of the file/folder being changed, created or deleted in the respective list boxes.

To clear a list box, the user has to select an item in that list box and click the ‘Clear’ button. The handler for the ‘Clear’ button is given below.

private void butclear_Click ( object sender, System.EventArgs e )
{
   if ( listcreate.SelectedIndex != -1 )
   listcreate.Items.Clear( ) ;
   else
      {
        if ( listchange.SelectedIndex != -1 )
        listchange.Items.Clear( ) ;
   else
        if ( listdelete.SelectedIndex != -1 )
        listdelete.Items.Clear( ) ;
      }
}

The SelectedIndex property returns –1 if no item is currently selected. If any item is selected, the condition becomes true and the list box gets cleared.

The following figure shows our application at work. The list boxes seem to have trapped a few files being changed.

In this article we will walk through the process of using the FileSystemWatcher component and watching the changes made to a subfolder/files of a selected folder.

The FileSystemWatcher component can keep track of creation, deletion, changing and renaming of a file/folder. It conveys to the application information about changes done to the file system by throwing events. It throws the Created, Deleted, Changed and Renamed events respectively. The name and path of the file/folder being changed is also made available in the event handlers.

The FileSystemWatcher component can watch files on a local computer, a network drive, or a remote computer. We can specify which files to watch by setting the appropriate value in the Filter property. If we wish to watch all the files we must set the Filter property to an empty string (“”). To watch a specific file, we must assign that filename to the Filter property. We can also use wildcards to specify certain type of file. For example, to watch for changes in EXE files, we can set the Filter property to “*.exe”.

The component has a property called NotifyFilter that can be used to specify the types of changes viz. changes in attribute, last write date and time, size, etc.

Having this much of knowledge about FileSystemWatcher component in hand, we can now use the component in our application.

We will create an application that uses the FileSystemWatcher control to keep watch on the folder selected by the user, an watch whether a file/folder is created, changed or deleted.

Create a WinForm application and put the controls on the form as shown in following figure.

We have added three list boxes to list the files/folders being created, changed or deleted. The ‘Watch Folder’ button allows the user to select a folder to watch. The path of the selected folder gets displayed on the label placed next to the ‘Watch Folder’ button. The ‘Clear’ button allows the user to delete the items listed in the list box having input focus.

In addition to these controls, add the FolderBrowserDialog control from the ‘Windows Forms’ tab and FileSystemWatcher component from the ‘Components’ tab of the ToolBox. The controls, their names and event handlers are given in the following table.

Add handlers for the Created, Deleted and Changed events. Also Set the IncludeSubdirectories property of the FileSystemWatcher component to true.

When the application is run, the user has to first select a folder to watch. He can do so by clicking the ‘Watch Folder’ button. We have displayed the ‘Browse For Folder’ standard dialog box in which user can select the folder. The dialog is displayed by calling the ShowDialog( ) method as shown below.

private void butwatch_Click ( object sender, System.EventArgs e )
{
   if ( browser.ShowDialog( ) == DialogResult.OK )
   {
      watcher.Path = browser.SelectedPath ;
      label1.Text = browser.SelectedPath ;
   }
}

We have specified the folder to watch by setting the Path property of the FileSystemWatcher class to the path of selected folder. The path of selected folder is retrieved from the SelectedPath property of the FolderBrowserDialog class. We have displayed the path on the label.

The handlers added for the FileSystemWatcher events are given below.

private void watcher_Changed ( object sender,
System.IO.FileSystemEventArgs e )
{
    listchange.Items.Add ( e.FullPath ) ;
}
    private void watcher_Created ( object sender,
System.IO.FileSystemEventArgs e )
{
    listcreate.Items.Add ( e.FullPath ) ;
}
   private void watcher_Deleted ( object sender,
System.IO.FileSystemEventArgs e )
{
   listdelete.Items.Add ( e.FullPath ) ;
}

In these handlers we have only added the full path of the file/folder being changed, created or deleted in the respective list boxes.

To clear a list box, the user has to select an item in that list box and click the ‘Clear’ button. The handler for the ‘Clear’ button is given below.

private void butclear_Click ( object sender, System.EventArgs e )
{
   if ( listcreate.SelectedIndex != -1 )
   listcreate.Items.Clear( ) ;
   else
  {
    if ( listchange.SelectedIndex != -1 )
    listchange.Items.Clear( ) ;
    else
    if ( listdelete.SelectedIndex != -1 )
    listdelete.Items.Clear( ) ;
  }
}

The SelectedIndex property returns –1 if no item is currently selected. If any item is selected, the condition becomes true and the list box gets cleared.

The following figure shows our application at work. The list boxes seem to have trapped a few files being changed.

Yashavant Kanetkar, one of the first Express Computer columnists, is an established software expert, speaker and author with several best-sellers to his credit, including titles like “Let Us C” and the “Fundas” series. Contact him at kanetkar@dcubesoft.com