how to comunicate among these objects
lazarus / 21-General

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Paolo · 2026-01-10 13:53

Hello
I have this

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TypeTA =
class(TObject)….End; and a lot of children

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TA1 =
class(TA)TA2 = class(TA)…TAi=class(TA).. Then I have also another
class TB that manages the above TAi.
Let say, as an example, I have something like this

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TypeTB =
class(TObject)   X : array of TA;  ..End; 
All went fine, unless… I have the need that one of TAi, let say TAn,
needs to access a field of TB !!!
I solved the problem in a very contrived way, any suggestions from the
experts ?

Regards

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cdbc · 2026-01-10 14:32

Hi
Introduce the "Owner Mechanism":Code: Pascal
 [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i type  {
forward decl. }  TB = class;  { the 'owned' class }  TA =
class(TObject)  private    fOwner: TB;  public    { in the constructor
we assign 'anOwner' to 'fOwner' }    constructor Create(anOwner: TB); 
...  end;  { actual TB class }  TB = class(TObject)    X: array of
TA;  ...  end; ////////////var   Bobj: TB;...  Bobj:= TB.Create; 
SetLength(Bobj.X,5);  Bobj.X[0]:= TA.Create(Bobj); /// create with
owner...  /// later one can do:  Bobj.X[0].fOwner.DoSomething(); A
full fledged example of this can be seen in "TCollection" &
"TCollectionItem"
Take a good hard long look at the source of TCollection... 
Regards Benny

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Thaddy · 2026-01-10 15:15

Alternatively derive from one of the generic object lists and define
the root of your class from TComponent, which is where the owner
property is introduced.

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Paolo · 2026-01-11 17:06

thank you very much.

At the end my code is very close to what you suggest. Essentially I
introduce a "father" of TB exposing only the thing that TAn needs,
something like

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i TBFather =
class(TObject)  function DoSomething : integer;end; TA =
class(TObject)  //blah, blah..End; { TAn } TAn = class(TA)  Ref :
TBFather;  Constructor CreateWithRef(ARef : TBFather);  function
DoSomething : integer;  // other fields hereend; TB = class(TBFather) 
AB : TAn;  // other fields hereend; implementation  constructor
TAn.CreateWithRef(ARef: TBFather);begin  inherited Create; 
Ref:=ARef;end; function TAn.DoSomething: integer;begin 
result:=Ref.DoSomething;end;

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jamie · 2026-01-11 23:13

Hmm, that kind of looks convoluted

Not really sure what you are after however, if you base them from the
TPersistent class, you could employ the notifiers that live there and
those
classes can notify each other when changes are taking place.

 Those would be the Observer and Observed items I am talking about.


Jamie