[DUG] call a method function from outside object

[Ross Levis]

I've spent a lot of time trying to work out a solution and discussing it 
on other mailing lists and newsgroups and it does not appear possible.

DLLOpen is declared as a standard procedure, not a method in the 3rd 
party C++ DLL, so if there are 2 instances of my component on the form, 
with 2 DLL's loaded, my component doesn't know which instance the DLL is 
calling, since a standard procedure occupies the same memory location in 
both instances of the component.

I've got around the problem by creating 3 identical sets of global 
procedures and using a global incrementing integer in the constructor, 
so each new instance is given a different procedure address.  The object 
instance pointers are stored in a global array so the procedure knows 
which instance of the object to work with. eg.

var
  ObjCount: Integer;
  MyObjects: array[1..3] of TMyObject

constructor Create;
begin
  Inc(ObjCount);
  MyObjects[ObjCount] := Self;
  case ObjCount of
    1: DLLOpen := Open1;
    2: DLLOpen := Open2;
    3: DLLOpen := Open3;
  end;
end

procedure Open1(SRate,nChan,BPS:Integer):Integer; cdecl;
begin
  MyObjects[1].Open(SRate,nChan,BPS);
end;

procedure Open2(SRate,nChan,BPS:Integer):Integer; cdecl;
begin
  MyObjects[2].Open(SRate,nChan,BPS);
end;

procedure Open3(SRate,nChan,BPS:Integer):Integer; cdecl;
etc

This limits the number of times a user can put my component on a form, 
but at least it works, and any more than 3 should not be necessary.

It would be nice if there was some way to translate a procedure call to 
one address and map it to a different address transparently to the 
calling DLL, then it could be fully OOP.  But I don't know if this is 
possible.

Regards,
Ross.

----- Original Message ----- 
From: <Guy.Brown at sungard.com>
To: <delphi at ns3.123.co.nz>
Sent: Monday, July 11, 2005 3:24 PM
Subject: RE: [DUG] call a method function from outside object


Hi Ross.  My Delphi is a bit rusty but I believe it's just:

DLLOpen := Open;

Assuming that DLLOpen is declared as a procedure of object with the
appropriate parameter list.

hth

Guy

-----Original Message-----
From: delphi-bounces at ns3.123.co.nz [mailto:delphi-bounces at ns3.123.co.nz]
On Behalf Of Ross Levis
Sent: Sunday, 3 July 2005 5:48 p.m.
To: NZ Borland Developers Group - Delphi List
Subject: Re: [DUG] call a method function from outside object

In trying to solve this I thought of using method functions inside an
object rather than standard functions, and then assigning the method
pointer to the DLL, but I can't seem to do this either.  eg. In a class
procedure I do this...

  DLLOpen := TMethod(Open).Code;  <<< Invalid typecast

Open is a function defined in the same class DLLOpen is the function
pointer defined in the DLL which I need to assign to the method pointer.

I'm not sure why this doesn't work.  My only other option is to use
global variables!

Regards,
Ross.

----- Original Message -----
From: "Ross Levis" <ross at stationplaylist.com>
To: "NZ Borland Developers Group - Delphi List" <delphi at ns3.123.co.nz>
Sent: Sunday, July 03, 2005 4:56 PM
Subject: [DUG] call a method function from outside object


In a component I'm writing, a DLL needs access to a standard function so
this is declared outside the main object.  Within this function I want
to access variables and methods inside the main object, but I can't find
a way to do it.  Is this possible?

Thanks,
Ross.

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