Hi,

I'd like to manage a list of heterogenous objects. For instance, I have a list of objects to buy in store: cheeses (of class TCheese), soaps (of class TSoap), flowers (of class TFlower), etc...

I thought to gather pointers to different objects of these classes in a TList. But, when it comes to manipulate or destroy these items, I am in trouble: I have lost the information about the precise type of the object the pointer points to.

Does somebody have an idea?

Thanks in advance,
Gilles Marcou

Use TObjectlist from contnrs.pas

Michael.

Like this :
(I can make a complete example if needed)

type
   TNodeAbstract = class
      procedure print;virtual;abstract;
   end;
   TNodeFoo = class(TNodeAbstract)
      procedure print;override;
      procedure SpecificMethodeForFoo;
   end;

...

var objs: TObjectList;
objs := TObjectList.Create(True);
objs.Add(TNodeFoo.Create);

...

var o : TNodeAbstract;
for i := 0 to objs.Count - 1 do begin
    o := TNodeAbstract(Objs[i]);
    if (o is TNodeFoo) then
       (o as TNodeFoo).SpecificMethodeForFoo;
    o.Print;
end;

Hi all,

thanks for your kind and fast answer. Effectively, TObjectList is what I need. Thanks to Damien, I understand a bit better how it works. But in my case I believe that I need to use some kind of TList of TObjectList. So is it possible to build a class that will have TObjecList member so that I will be able to use TList of this class?

For instance:

-----
TToDo=class(TList)
private
   fProducts: TObjectList;//Cheeses, Soaps, etc.
   fShops: TObjectList;//Shops, Markets, Internet,...
public
   property Products: TObjectList read fProducts write fProducts;
   property fShops: TObjectList read fShops write fShops;
   creator Create;
   destructor Destroy; override;
   procedure Clear; override;
   ...
end;
-----

I may have to say more about my project so you'll have better insight in my design problem. I have an XML to drive my application to do a set of diverse actions.

Root
|
|-action1-|-action11
| |-action12
|
|-action2-|-action21
|-action22

action1 and action2 shall be a TObjectList because action11, action12,... can be instances of different classes. Then I want action1 and action2 to be stored in some kind of container (I believe a TList).

So I call to your opinion to see if it is an acceptable design and if I am not mixing incompatible concepts (TList and TObjectList).

Thanks for your insight,
Gilles Marcou

No. Per node you can add its own ObjectList and use virtual methods to make the job for you.