c# - Alex FTPS getting callback from PutFile -

i'm using alex ftps upload file. result message putfile command.

i see there filetransfercallback don't know how use exactly.

using (ftpsclient client = new ftpsclient())             {                 // connect server                 client.connect(ftpserver, new networkcredential(ftpuser, ftppwd),                            esslsupportmode.credentialsrequired | esslsupportmode.datachannelrequested | esslsupportmode.implicit,                             new remotecertificatevalidationcallback(validatetestservercertificate) );                 client.settransfermode(etransfermode.binary);                  // upload file                 myresult += client.putfile(filename, fi.name, filetransfercallback???);             } 

how info filetransfercallback?