[DUG] Interfaces

[Alister Christie]

I'm having some fun with interfaces

I have two interfaces IXMLResidentialType and IAuctionable.
I have a class which implements these two interfaces
TXMLResidentialType = class(TXMLNode, IXMLResidentialType, IAuctionable) 
...

I have some code
var
  Res : IXMLResidentialType;
  Auctionable : IAuctionable;
begin
...
  if Res.QueryInterface(IAuctionable, Auctionable) = 0 then
    ShowMessage('Auctionable');

What I'm trying to determine is if Res implements IAuctionable - which 
it does (through TXMLResidentialType which effective Res is an instance 
of), however IXMLResidentialType doesn't seem to realise this.  How do I 
make this work?

Does this question make any sense?

If I'm not able to do this it's not too much of a problem, but will mean 
a bunch of duplicated code.


-- 
Alister Christie
Computers for People
Ph: 04 471 1849 Fax: 04 471 1266
http://www.salespartner.co.nz
PO Box 13085
Johnsonville
Wellington