Dear Todd
My understanding is that interfaces inherit transparently (as you would
expect). QueryInterface should give you the answer you need.
A return result of 0 means success. An additional benefit is it does a
safe cast for you at the same time.
e.g.
if NewObject.QueryInterface(IFirstDescendant, tmp) <> 0 then raise
exception.Create('Invalid FirstDecebdant object')
else
begin
tmp.foo;
end;
Stephen
> -----Original Message-----
> From: Todd Martin [mailto:[EMAIL PROTECTED]
> Sent: Friday, 13 June 2003 1:53 p.m.
> To: Multiple recipients of list delphi
> Subject: [DUG]: Interface Inheritance
>
>
> Hi
>
> Does anyone know if there's a way to test for interface
> inheritance? For example
>
> IFirstDescendant = interface(IInterface);
> ISecondDescendant = interface(IFirstDescendant);
>
> TNewClass = class(TInterfacedObject,ISecondDescendant);
>
> NewObject = TNewClass.Create;
>
> is there a way to see whether NewObject supports the
> interface "IFirstDescendant"
>
> NewObject.GetInterface(IFirstDescendant,Descendant)
> returns a nil pointer for Descendant.
>
> I'm thinking the VTable entry for the ISecondDescendant
> interface, might link back to IFirstDescendant somehow.
>
> Todd.
>
>
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