Triggering other events within OnCreate handler

[simsee]

Consider the following program:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ExtCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Shape1: TShape;
16.     procedure FormCreate(Sender: TObject);
17.     procedure Shape1ChangeBounds(Sender: TObject);
18.   private
19.  
20.   public
21.  
22.   end;
23.  
24. var
25.   Form1: TForm1;
26.  
27. implementation
28.  
29. {$R *.lfm}
30.  
31. { TForm1 }
32.  
33. procedure TForm1.FormCreate(Sender: TObject);
34. begin
35.   Shape1.Left:=Shape1.Left+100;
36. end;
37.  
38. procedure TForm1.Shape1ChangeBounds(Sender: TObject);
39. begin
40.   Caption:='ok';
41. end;
42.  
43. end.

Changing Shape1.Left within OnCreate does not trigger Shape1ChangeBounds.

Differently, changing Shape1.Left within OnShow triggers Shape1ChangeBounds, as in the following program:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ExtCtrls;
9.  
10. type
11.  
12.   { TForm1 }
13.  
14.   TForm1 = class(TForm)
15.     Shape1: TShape;
16.     procedure FormShow(Sender: TObject);
17.     procedure Shape1ChangeBounds(Sender: TObject);
18.   private
19.  
20.   public
21.  
22.   end;
23.  
24. var
25.   Form1: TForm1;
26.  
27. implementation
28.  
29. {$R *.lfm}
30.  
31. { TForm1 }
32.  
33. procedure TForm1.FormShow(Sender: TObject);
34. begin
35.   Shape1.Left:=Shape1.Left+100;
36. end;
37.  
38. procedure TForm1.Shape1ChangeBounds(Sender: TObject);
39. begin
40.   Caption:='ok';
41. end;
42.  
43. end.

Why this different behavior?

I ask because I would need to intercept all changes to the Left and Top properties of a component I'm writing, even those that happen within OnCreate events of the parent control. Left and Top have getters and setters that are not virtual and this prevents me from redefining them in descending control.

Any suggestions? Thanks!

[ASerge]

Why this different behavior?

Answer in procedure TControl.CheckOnChangeBounds (see my comment):

Code: Pascal  [Select][+][-]

1. begin
2. ...
3.   if (not CompareRect(@FLastDoChangeBounds,@CurBounds)) or (ComparePoints(CurClientSize,FLastDoChangeClientSize)<>0) then begin
4.     if FormIsUpdating then begin // <- This True in OnCreate and False in OnShow
5.       Include(FControlFlags,cfOnChangeBoundsNeeded);
6.       exit; // Exit when OnCreate
7.     end;
8.     FLastDoChangeBounds:=CurBounds;
9.     FLastDoChangeClientSize:=CurClientSize;
10.     DoOnChangeBounds; // So, not called when OnCreate
11.   end;
12.  

[simsee]

Thanks ASerge. The code snippet makes it clear the reason for the different behavior.

Is there a way to ensure that all changes to Left,Top,Width and Height in a TControl derived component are also "intercepted" in the parent/owner's OnCreate event handlers?

[simone]

I would override TControl.Resize TControl.ChangeBounds method, which is virtual, as in the following code:

Code: Pascal  [Select][+][-]

1. unit Unit1;
2.  
3. {$mode objfpc}{$H+}
4.  
5. interface
6.  
7. uses
8.   Classes, SysUtils, Forms, Controls, Graphics, Dialogs, ExtCtrls;
9.  
10. type
11.  
12.   { TShape }
13.  
14.   TShape=class(ExtCtrls.TShape)
15.   protected
16.     procedure ChangeBounds(ALeft: Integer; ATop: Integer; AWidth: Integer; AHeight: Integer; KeepBase: Boolean); override;
17.   end;
18.  
19.   { TForm1 }
20.  
21.   TForm1 = class(TForm)
22.     Shape1: TShape;
23.     procedure FormCreate(Sender: TObject);
24.   private
25.  
26.   public
27.  
28.   end;
29.  
30. var
31.   Form1: TForm1;
32.  
33. implementation
34.  
35. {$R *.lfm}
36.  
37. { TShape }
38.  
39. procedure TShape.ChangeBounds(ALeft: Integer; ATop: Integer; AWidth: Integer; AHeight: Integer; KeepBase: Boolean);
40. begin
41.   inherited;
42.   writeln('ok');
43. end;
44.  
45. { TForm1 }
46.  
47. procedure TForm1.FormCreate(Sender: TObject);
48. begin
49.   Shape1.Left:=Shape1.Left+100;
50. end;
51.  
52. end.