Comments on: Getting an interface back out of a Variant http://blog.excastle.com/2005/07/06/getting-an-interface-back-out-of-a-variant/ Life, .NET, and Cats Tue, 31 Aug 2010 13:47:10 +0000 http://wordpress.org/?v=2.9.2 hourly 1 By: Joe White's Blog http://blog.excastle.com/2005/07/06/getting-an-interface-back-out-of-a-variant/comment-page-1/#comment-5391 Joe White's Blog Sun, 10 Jul 2005 15:02:00 +0000 http://blog.excastle.com/2005/07/06/getting-an-interface-back-out-of-a-variant/#comment-5391 <strong>Pathological QueryInterfaces</strong> Pathological QueryInterfaces

]]> By: Sebastian http://blog.excastle.com/2005/07/06/getting-an-interface-back-out-of-a-variant/comment-page-1/#comment-5390 Sebastian Sat, 09 Jul 2005 09:57:00 +0000 http://blog.excastle.com/2005/07/06/getting-an-interface-back-out-of-a-variant/#comment-5390 Have you tested that Supports() puts nil to the "out Intf" parameter if the interface is NOT supported? <br>This isn't really clear from the docs so I would recommend <br> <br>function VariantAsIFoo(V: Variant): IFoo; <br>begin <br> Result:=nil; <br> if VarIsType(V, varUnknown) then <br> Supports(V, IFoo, Result); <br>end; <br> <br>or if you don't like unnecessary assignments <br> <br>function VariantAsIFoo(V: Variant): IFoo; <br>begin <br> if VarIsType(V, varUnknown) then <br> begin <br> if not Supports(V, IFoo, Result) then <br> Result:=nil; <br> end else <br> Result := nil; <br>end; <br> <br>Anyway thanks for sharing! I really enjoy reading your blog! Have you tested that Supports() puts nil to the "out Intf" parameter if the interface is NOT supported?

This isn’t really clear from the docs so I would recommend

function VariantAsIFoo(V: Variant): IFoo;

begin

Result:=nil;

if VarIsType(V, varUnknown) then

Supports(V, IFoo, Result);

end;

or if you don’t like unnecessary assignments

function VariantAsIFoo(V: Variant): IFoo;

begin

if VarIsType(V, varUnknown) then

begin

if not Supports(V, IFoo, Result) then

Result:=nil;

end else

Result := nil;

end;

Anyway thanks for sharing! I really enjoy reading your blog!

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