Solved

Constructor on TObject descendant

Posted on 2004-04-01
9
524 Views
Last Modified: 2013-11-23
The cReate for a TObject descendant is not getting fired, in fact it's not trecognised by the complier (no blue dots). here's some sample code. What have I done wrong?

Thanks, Tom.

  TOne = class(TObject)
  private
  protected
  public
  published
  end;


  TTwo = class(TOne)
  private
    Flbl : TLabel;
  protected
  public
    constructor create;
    destructor destroy; override;
  published
  end;

constructor TTwo .create;
begin
  inherited create;

  Flbl := TLabel.Create(nil);
end;

destructor TTwo .destroy;
begin
  Flbl.free;
  inherited;
end;
0
Comment
Question by:tomcorcoran
  • 4
  • 3
  • 2
9 Comments
 
LVL 12

Expert Comment

by:esoftbg
ID: 10730735
unit Unit_Q_20939766;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TOne = class(TObject)
    private
    protected
    public
    published
  end;

  TTwo = class(TOne)
    private
      Flbl : TLabel;
    protected
    public
      constructor create;
      destructor destroy; override;
    published
  end;

  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    private { Private declarations }
    public  { Public declarations }
  end;

var
  Form1: TForm1;
  Two:   TTwo;

implementation

{$R *.dfm}

constructor TTwo .create;
begin
  inherited create;

  Flbl := TLabel.Create(nil);
end;

destructor TTwo .destroy;
begin
  Flbl.free;
  inherited;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Two := TTwo.Create;
  Two.Flbl.Parent := Self;
  Two.Flbl.Caption := 'Hello everybody';
end;

end.

emil
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 10730752
>in fact it's not trecognised by the complier (no blue dots).
In my test example it is recognised by compiler and works ?
I see the caption of Flbl on my form....

emil
0
 

Author Comment

by:tomcorcoran
ID: 10730821
Ok, not sure what I've missed here :-) Must be something else in my code I am missing.

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls;

type
  TOne = class(TObject)
    private
    protected
    public
    published
  end;

  TTwo = class(TOne)
    private
      Flbl : TLabel;
    protected
    public
      constructor create;
      destructor destroy; override;
    published
  end;


  TThree = class(TTwo)
    private
      Flbl2 : TLabel;
    protected
    public
      constructor create;
      destructor destroy; override;
    published
  end;

  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    procedure FormDestroy(Sender: TObject);
    private { Private declarations }
    public  { Public declarations }
  end;

var
  Form1: TForm1;
  Two:   TTwo;
  Three:   TThree;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
begin
  Two := TTwo.Create;
  Two.Flbl.Parent := Self;
  Two.Flbl.Caption := 'Hello everybody';

  Three := Three.Create;
  Three.Flbl.Parent := Self;
  Three.Flbl.Caption := 'Ya know it';
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  Three.Free;
  Two.Free;
end;

{ TTwo }

constructor TTwo.create;
begin
  inherited create;

  Flbl := TLabel.Create(nil);
end;

destructor TTwo.destroy;
begin
  Flbl.free;
  inherited;
end;

{ TThree }

constructor TThree.create;
begin
  inherited create;

  Flbl2 := TLabel.Create(nil);
end;

destructor TThree.destroy;
begin
  Flbl2.free;
  inherited;
end;



end.

 I get no blue dots on the last destructor :

destructor TThree.destroy;
begin
  Flbl2.free;
  inherited;
end;
0
 
LVL 12

Accepted Solution

by:
esoftbg earned 50 total points
ID: 10730875
here are blue dots:

unit Unit_Q_20939766;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls,
  Forms, Dialogs, StdCtrls;

type
  TOne = class(TObject)
    private
    protected
    public
    published
  end;

  TTwo = class(TOne)
    private
      Flbl : TLabel;
    protected
    public
      constructor Create(AOwner: TWinControl); dynamic;
      destructor  Destroy; override;
    published
  end;

  TThree = class(TTwo)
    private
      Flbl2 : TLabel;
    protected
    public
      constructor Create(AOwner: TWinControl); override;
      destructor Destroy; override;
    published
  end;

  TForm1 = class(TForm)
    procedure FormCreate(Sender: TObject);
    private { Private declarations }
    public  { Public declarations }
  end;

var
  Form1: TForm1;
//  Two:   TTwo;
  Three: TThree;

implementation

{$R *.dfm}

constructor TTwo.Create(AOwner: TWinControl);
begin
  inherited Create;
  Flbl := TLabel.Create(AOwner);
  Flbl.Parent := AOwner as TWinControl;
end;

destructor TTwo.Destroy;
begin
  Flbl.Free;
  inherited;
end;

constructor TThree.Create(AOwner: TWinControl);
begin
  inherited Create(AOwner);
  Flbl2 := TLabel.Create(AOwner);
  Flbl2.Parent := AOwner as TWinControl;
end;

destructor TThree.Destroy;
begin
  Flbl2.Free;
  inherited;
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  Three := TThree.Create(Self);
  Three.Flbl.Font.Style := [fsBold];
  Three.Flbl.Font.Size := 16;
  Three.Flbl.Left := 128;
  Three.Flbl.Top := 96;

  Three.Flbl2.Font.Style := [fsBold];
  Three.Flbl2.Font.Size := 16;
  Three.Flbl2.Left := 128;
  Three.Flbl2.Top := 128;

  Three.Flbl.Caption := 'Hello everybody';
  Three.Flbl2.Caption := 'Ya know it';
end;

end.
0
Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

 
LVL 22

Expert Comment

by:Ferruccio Accalai
ID: 10730890
you're calling create inheriting it but how can you inherit a non overrided procedure? It's never inherited so....

override the TTwo and TThree constructor procedures....
0
 

Author Comment

by:tomcorcoran
ID: 10730925
How can you override the constructor since it's not virtaul in TObject?
0
 
LVL 12

Expert Comment

by:esoftbg
ID: 10731030
//.........
    public
      constructor Create(AOwner: TWinControl); dynamic;
//.........
0
 
LVL 22

Expert Comment

by:Ferruccio Accalai
ID: 10731049
ah sorry, of course...missed that it's descending from TObject....esoftbg gave the right answer....declaring it dynamic
0
 

Author Comment

by:tomcorcoran
ID: 10731070
Something is wrong in my setip. The framework takes care of creating the object and somehow the "middle" create is missed.

Cheers, Tom.
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

The uses clause is one of those things that just tends to grow and grow. Most of the time this is in the main form, as it's from this form that all others are called. If you have a big application (including many forms), the uses clause in the in…
Creating an auto free TStringList The TStringList is a basic and frequently used object in Delphi. On many occasions, you may want to create a temporary list, process some items in the list and be done with the list. In such cases, you have to…
This video explains how to create simple products associated to Magento configurable product and offers fast way of their generation with Store Manager for Magento tool.
Need to grow your business through quality cloud solutions? With everything required to build a cloud platform and solution, you may feel like the distance between you and the cloud is quite long. Help is here. Spend some time learning about the Con…

939 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

10 Experts available now in Live!

Get 1:1 Help Now