How to cast List to a derived class of T

Question

AnswerRecords return a list of DnsRecordBase:

List<DnsRecordBase> _Records = _DnsMessage.AnswerRecords;

MxRecord inherit from DnsRecordBase:

public class MxRecord : DnsRecordBase

How to cast _Records has a list of MxRecord ?

I have tried:

List<MxRecord> _Records = (MxRecord)_DnsMessage.AnswerRecords;
List<MxRecord> _Records = _DnsMessage.AnswerRecords as MxRecord;

This syntaxes doesn't work :)

@nvoigt While that answers the question, that's not actually duplicate that is exactly other way around — Sriram Sakthivel, Jan 04 '14 at 12:02

score 4 · Accepted Answer · answered Jan 04 '14 at 11:59

4

This should work if all elements in _Records are MxRecord

List<DnsRecordBase> _Records = _DnsMessage.AnswerRecords;
List<MxRecord> _MxRecords = _Records.Cast<MxRecord>().ToList();

answered Jan 04 '14 at 11:59

Sriram Sakthivel

if they're not all of type MxRecord, you can use the `Enumerable.OfType()` method to get only items that are MxRecords – Lorentz Vedeler Jan 04 '14 at 12:35
Thanks that work. I did not know the cast method. So in one line : `List _Records = _DnsMessage.AnswerRecords.OfType().Cast().ToList();` – user2705397 Jan 04 '14 at 13:04
1

If you use `OfType` you don't need a cast then – Sriram Sakthivel Jan 04 '14 at 13:05

1 Answers1