Capture EVN-1, PID-3, PV1-2, FT1-2 to file

How can I capture a list of the following fields: EVN-1, PID-3, PV1-2, FT1-2 in a comma delimited list?
Custom code is the best approach if you are expecting repeated FT1 segments. The following code will create a file in the c:\temp directory containing the specified list, and will display in Notepad upon completion.

string _fileName = @"c:\temp\_test.txt";
StreamWriter _file;

public override void Run() {
  // Get an HL7 Message in parsed format
  HL7Message message = GetParsedMessage();
  // Get the first FT1 segment
  EVN evn = message.Segments.OfType<EVN>().FirstOrDefault();
  PID pid = message.Segments.OfType<PID>().FirstOrDefault();
  PV1 pv1 = message.Segments.OfType<PV1>().FirstOrDefault();
  foreach(FT1 ft1 in message.Segments.OfType<FT1>())
    _file.Write("{0},",evn != null ? evn.EventTypeCode_01.Value : null);
    _file.Write("{0},",pid != null ? pid.PatientIdentifierList_03.First.Value : null);
    _file.Write("{0},",pv1 != null ? pv1.PatientClass_02.Value : null);
    _file.Write("{0},",ft1 != null ? ft1.TransactionID_02.Value : null);

public override void OnStart()
  // create the file to be written out
  _file = new StreamWriter(_fileName,false);

// Called once after the last message has been processed.
// It is a good place to perform cleanup and to report information.
// Always called from the UI thread.
public override void OnFinish() {
  // sort the data
  // launch notepad to display the file.