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Acces to internal data from a COM interface.

Posted on 1998-04-06
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Last Modified: 2010-05-18
I've written a function that has 2 interfaces IObj1 en IObj2 for parameters.  The interfaces are related to a COM object OBJ.  This OBJ has an integer variable in his private section.  How can I access this integer from IObj1 or IObj2, without declaring additional  methods in the interfaces.  
This is a simplification of the problem.   The answer has to work for strings, double and even objects.
I already know the tricj with the GetInterfaceEntry etc... .  Is there a clean solution to this problem ?

Johan
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Question by:ppr
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AndersWP earned 450 total points
ID: 1361307
You can not directly access internal variables of a COM object, you have to go through an interface; that is the fundamental principle of COM.

If you wnat to access an integer in a COM object and you do not want to enlarge your existing interfaces IObj1 and IObj2 (or whatever they are called), you can define a new interface:


IMyPrivateInteger = Interface
  [IMyPrivateInteger_GUID]
  Function GetValue: Integer;
End;

TMyObject = Class(BaseClass, IMyPrivateInteger, IObj1, iObj2)
Private
  FMyInteger: Integer;
Public
  Function GetValue: Integer;
  ...
End;

If you have e.g. an IObj1 interface to your object, you can get access the integer variable like this:

Var
  MyPrivateInteger: IMyPrivateInteger;

Begin
  Obj1.QueryInterface(IMyPrivateInteger_GUID,
                      MyPrivateInteger);
  i:=MyPrivateInteger.GetValue;
End;

Not exactly simple, but it should work. Note that you will have make interface methods for retrieving each of the private fields that you want to expose.

I hope this will help you.

Greetings,
AndersWP
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