Hi All!

I have an app that uses a TTabControl to select the display of one of many objects. The code is really trivial in the real app, but I have further simplified it to the bare essentials:

unit Unit1;
{$mode objfpc}{$H+}
interface

uses
Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, StdCtrls,

   ComCtrls;

type
   { TForm1 }
   TForm1 = class(TForm)
     Button1: TButton;
     Label1: TLabel;
     TabControl1: TTabControl;
     procedure Button1Click(Sender: TObject);
     procedure TabControl1Change(Sender: TObject);
   private
     { private declarations }
     N : Integer;
   public
     { public declarations }
   end;
var
   Form1: TForm1;
implementation
{$R *.lfm}

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);
begin
   Inc(N);
   TabControl1.Tabs.AddObject(IntToStr(N),TObject(N));
end;
procedure TForm1.TabControl1Change(Sender: TObject);
var
   I : Integer;
begin
   I := TabControl1.TabIndex;
   Label1.Caption := IntToStr(Integer(TabControl1.Tabs.Objects[I]));
end;
end.

Pressing Button1 adds consecutively-numbered tabs a tab SHOULD set Label1's caption to the number on the tab (and DOES when used with Delphi). It actually outputs non-consecutive numbers in the 37,000,000 range. I get similar results using Windows, OSX and Debian.

In the real app, I use an object with a name, but when I select a tab, it goes somewhere in the address space (not sure where in the context of the app) and returns a string of un-printable characters as the name (and other random values for the remaining contents of the object).

As I said above, the exact same code in Delphi (2006 and 2007) works as expected, but obviously is limited to Windows.

I tried similar operations with a TListBox and the object was returned correctly so I don't think the problem is with TStrings or its descendents.

Any help would be appreciated.

Don Ziesig

P.S. I have tried to find the LCL code and debug the library myself but I must be missing something in my searches. Some pointers in that area would also be appreciated.

AFAIR the Tabs.Objects property is implemented differently from Delphi, i.e. the LCL doesn't support it at all :-(

Chances for an fix are low, because the LCL TabControl is based on the gtk implementation, that differs widely from the Win32 ComCtrls implementation.

P.S. I have tried to find the LCL code and debug the library myself but I must be missing something in my searches. Some pointers in that area would also be appreciated.

Controls have their high-level interface in the LCLBase package, e.g. "class TTabControl" in lcl\ComCtrls.pp, and their associated widget in e.g. lcl\interfaces\win32\win32wscomctrls.pp.

DoDi