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Ah I see, I realise your problem now.
What I was suggesting with regards to the casting,
would be something like this.
dllobject.tag:=3; (or classname or whatever you
want to use).
dllobject.passobject(someobject);
inside dll.
var PanelObject:tpanel;
ButtonObject:tbutton;
procedure
passobject(someobject:tobject);
begin
case someobject.tag
of
1:begin
PanelObject:=tpanel(someobject);
Objecttype:=1;
end;
2:begin
ButtonObject:=tbutton(someobject);
Objecttype:=3;
end;
end;
function Useditem:tobject;
begin
case
objecttype of
1:result:=panelobject;
3:result:=buttonobject;
end;
end;
If you do it this way, then statements such as if
Useditem is twhatever, should work, actually after having read your last email,
Im not so sure now?
I realise this is very limited because you have to
hard code the dll to handle specific object types. If you had say 3 different
types of objects
I may be suggesting things that don't suit what you
are trying to achieve, because Im not sure on what types of objects you are
passing through, how many different types there are, whether the number of types
of these would change etc...
For example if the object type was one of your own,
I would tend to suggest a rider class that would pass all the information on to
the dll in the form of a stream. I have routines that does this, and then reads
the object type from the stream and then applies the appropriate reader and
writer class, but it would depend completely on what you were trying to achieve.
It still requires having to write an interface to each object type
though.
Just some thoughts, hope you sort it
out,
Matt.
----- Original Message -----
Sent: Wednesday, September 08, 2004 5:46
PM
Subject: Re: [DUG] Passing Objects to a
DLL
Hi Matt, casting doesn't actually work when you
are trying to compare class types since you don't know what class you have
anyway. The tag idea may as well just be the the classname which is what we
use as a workaround anyway. If an object is passed into a dll it's fine since
it shares the same application space, but I think the issue is with the run
time type information that Delphi uses. For example if I use the debugger to
have a look at a class variable passed into a dll, it doesn't give the
classname, it give something like TClass($4F801) (except a real memory
address).
Thanks anyway.
Cheers,
Phil.
----- Original Message -----
Sent: Wednesday, September 08, 2004
4:54 PM
Subject: Re: [DUG] Passing Objects to a
DLL
Hey Phil, as you know doubt know, passing any
type of memory around that is dynamic (e.g. string) as apposed to static
(e.g. integer) is not a good idea. I haven't looked but maybe this class
information uses strings to store different things, and therefore is
unreliable.
How many different types of object are you
passing through? could you perhaps set the object tag value (e.g. tag=1 =
twhatever tag=2 = twhatever2 and then cast type within the dll? ) This
would mean though that you would have to upgrade your dll if you want to
support any additional type of objects.
By the way, I would recommend you not doing
this at all. I would pass what information you need from the object through
in a static object type, create an object of the type required within the
dll and do what you have to do, but of course that would completely depend
on the type of object you are throwing around.
Matt.
----- Original Message -----
Sent: Wednesday, September 08, 2004
4:47 PM
Subject: [DUG] Passing Objects to a
DLL
When an object is passed to a DLL it comes
across fine and all properties and methods can be accessed, but somehow
the class information gets handled differently. Using the
"is" comparison fails when it should work - even InheritsFrom doesn't
work. We've got around this in the past by using a recursive routine to
compare class/ancestor names but I'm beginning to wonder if there is a
trick that I have missed somewhere.
Can anyone shed any light on
this?
Cheers,
Phil.
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