Xceed .NET Libraries Documentation
How to manually parse listing lines

Welcome to Xceed .NET, .NET Standard and Xamarin Libraries! > Task-Based Help > FTP capabilities > Working with the FtpClient interface > How to manually parse listing lines

Xceed FTP for .NET currently provides automatic support for listing the contents of AS400, DOS (Windows), UNIX and VMS FTP servers when calling the GetFolderContents method of the FtpClient class or the BeginGetFolderContents/ EndGetFolderContents methods of the AsyncFtpClient class. To modify or manually parse the listing lines returned by the FTP server, the ParsingListingLine event can be used, or a new listing parser added to the FTP client's ListingParsers collection. 

Usually, if you only want to modify or filter the listing lines returned by the GetFolderContents or BeginGetFolderContents/EndGetFolderContents methods, you would handle the ParsingListingLine event rather than creating a listing parser. If however you want to support the listing lines returned by an FTP server that is not automatically supported by Xceed FTP for .NET, then your best option would be to create a listing parser as it will make it easier to reuse your code. 

AsyncFtpClient's methods now call the corresponding synchronous methods on a background thread. For this reason, the AsyncFtpClient class is now considered obsolete. It is therefore recommended to use FtpClient instead to improve code readability.
When using Xceed FTP for .NET in a WinForms application, it is recommended that a SynchronizingObject be assigned to the SynchronizingObject property of the FtpClient class. For more information, jump to the WinForms applications and threading topic.  

To create a custom listing parser, create a class that derives from the FtpListingParser class and override the ParseLine method. In the ParseLine method, parse the line that is received as a parameter to create and return a new FtpItemInfo object that contains the FTP item's information. Once you have your custom listing parser, add it to the FTP client's ListingParsers collection. 

The GetFolderContents and BeginGetFolderContents/EndGetFolderContents methods retrieve the entire (or filtered) contents of the FTP server's current working folder. 

If you want to retrieve the contents of another folder, you could use the ChangeCurrentFolder or BeginChangeCurrentFolder/ EndChangeCurrentFolder methods, or ChangeToParentFolder or BeginChangeToParentFolder/ EndChangeToParentFolder methods to change the current working folder. The current working folder can be retrieved via the GetCurrentFolder or BeginGetCurrentFolder/ EndGetCurrentFolder methods. 

The ReceiveMultipleFiles and SendMultipleFiles method will also raise the ParsingListingLine event.

Synchronous (blocking) and asynchronous (non-blocking) demonstration using FtpClient

The following examples demonstrates how use the ParsingListingLine event to manually parse the listing lines returned by an FTP server to remove the potential   "." and ".." items. An asynchronous (non-blocking) demonstration is also available.

VB.NET Copy Code

Dim ftp As New FtpClient()

' When using FtpClient, you can instruct
' the library to automatically redirect events on the main UI thread
' by setting the SynchronizingObject property.
ftp.SynchronizingObject = Me

AddHandler ftp.ParsingListingLine, AddressOf Me.parsing_line

ftp.Connect( "localhost" )
ftp.Login()

ftp.GetFolderContents()

ftp.Disconnect()

RemoveHandler ftp.ParsingListingLine, AddressOf Me.parsing_line

Private void parsing_line( ByVal sender As Object, _
                           ByVal e As ParsingListingLineEventArgs )
  If( e.Item.Name = "." ) Or ( e.Item.Name = ".." ) Then
    e.Valid = False
  Else
    ListBox1.Items.Add( e.Item.Name )
  End If
End Sub

C# Copy Code
FtpClient ftp = new FtpClient();
 
// When using FtpClient, you can instruct
// the library to automatically redirect events on the main UI thread
// by setting the SynchronizingObject property.
ftp.SynchronizingObject = this;

ftp.ParsingListingLine += new ParsingListingLineEventHandler( this.parsing_line );
            
ftp.Connect( "localhost" );
ftp.Login();
            
ftp.GetFolderContents();
 
ftp.Disconnect();
 
ftp.ParsingListingLine -= new ParsingListingLineEventHandler( this.parsing_line );
            
private void parsing_line( object sender, ParsingListingLineEventArgs e )
{
  if( ( e.Item.Name == "." ) || ( e.Item.Name == ".." ) )
  {
    e.Valid = false;
  }
  else
  {
    listBox1.Items.Add( e.Item.Name );        
  } 
}

Asynchronous (non-blocking) demonstration

AsyncFtpClient's methods now call the corresponding synchronous methods on a background thread. For this reason, the AsyncFtpClient class is now considered obsolete. It is therefore recommended to use FtpClient and assign a SynchronizingObject to its SynchronizingObject property to improve code readability.

The following examples demonstrates how use the ParsingListingLine event to manually parse the listing lines returned by an FTP server to remove the potential   "." and ".." items. A synchronous (blocking) demonstration is also available. 

To clarify the code, instead of using callbacks, we will wait for completion of the operation before calling the matching "End" method. More information is available in the WinForms application and threading topic.

VB.NET Copy Code

Dim ftp As New AsyncFtpClient()

AddHandler ftp.ParsingListingLine, AddressOf Me.parsing_line

Dim result As IAsyncResult = ftp.BeginConnect("localhost", Nothing, Nothing)

While Not result.IsCompleted
  Application.DoEvents()
End While

ftp.EndConnect( result )
result = ftp.BeginLogin( Nothing, Nothing )

While Not result.IsCompleted
  Application.DoEvents()
End While

ftp.EndLogin( result )
result = ftp.BeginGetFolderContents( Nothing, Nothing )

While Not result.IsCompleted
  Application.DoEvents()
End While

ftp.EndGetFolderContents( result )
result = ftp.BeginDisconnect( Nothing, Nothing )

While Not result.IsCompleted
  Application.DoEvents()
End While

ftp.EndDisconnect( result )
RemoveHandler ftp.ParsingListingLine, AddressOf Me.parsing_line

Private Sub parsing_line(ByVal sender As Object, ByVal e As ParsingListingLineEventArgs)
  If (e.Item.Name = ".") Or (e.Item.Name = "..") Then
    e.Valid = False
  Else
    ListBox1.Items.Add(e.Item.Name)
  End If
End Sub

C# Copy Code
AsyncFtpClient ftp = new AsyncFtpClient ();
 
ftp.ParsingListingLine += new ParsingListingLineEventHandler( this.parsing_line );            
IAsyncResult result = ftp.BeginConnect( "localhost", null, null);
 
while( !result.IsCompleted )
  Application.DoEvents();
 
ftp.EndConnect( result );
result = ftp.BeginLogin( null, null);
 
while( !result.IsCompleted )
  Application.DoEvents();
            
ftp.EndLogin( result );
result = ftp.BeginGetFolderContents( null, null);
 
while( !result.IsCompleted )
  Application.DoEvents();
 
ftp.EndGetFolderContents( result );
result = ftp.BeginDisconnect( null, null);
 
while( !result.IsCompleted )
  Application.DoEvents();
 
ftp.EndDisconnect( result );
ftp.ParsingListingLine -= new ParsingListingLineEventHandler( this.parsing_line );
            
private void parsing_line( object sender, ParsingListingLineEventArgs e )
{
  if( ( e.Item.Name == "." ) || ( e.Item.Name == ".." ) )
  {
    e.Valid = false;
  }
  else
  {
    listBox1.Items.Add( e.Item.Name );        
  } 
}

Things you should consider

  • Are you using Xceed FTP for .NET in a WinForms application? Use the AsyncFtpClient class rather than the FtpClient class. 

  • Do you want to know the state of the FTP client? Check the Connected and Busy properties. You can also check the State property for specific state information. 

  • Do you want to prevent routers from prematurely closing the command channel while a long data transfer is taking place. Set the KeepAliveInterval property.

 

 

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