On Wed, 21 Dec 2005 20:28:55 +0200
Markku Niskanen <[EMAIL PROTECTED]> wrote:
> Hello,
>
> I have been trying to create a simple new component just for the
> sake of experience and I MUST be real stupid as I get the following
> backtrace when I try to insert the new component (which has been
> compiled ok) to the form. The component comes from Delphi and
> works just fine there.
>
> It seems to me as if the TWincontrol needed a parent but as it
> cannot find one simply raises an exception. Before getting into the
> real thing I created the simplest component I can image, it extends
> class TCustomPanel and onPaint it should draw a very short line
> and is totally useless. The Canvas operation Moveto() seems to
> start the chain.
>
> Any help would be appreciated. I do not mind being called an
> idiot, either :)
>
> When I get the first real component done I will document the
> process and publish it as a starter's tutorial.
>
> ----- gdb backtrace (running lazarus, dropping component) -----------
> Program received signal SIGFPE, Arithmetic exception.
> $0040dc98 in RAISEGDBEXCEPTION (MSG=$1f95e4c) at LCLProc.pas:594
> (gdb) bt
> #0 $0040dc98 in RAISEGDBEXCEPTION (MSG=$1f95e4c) at LCLProc.pas:594
> #1 $00480f45 in TWINCONTROL__CREATEWND (this=$2216928) at
> wincontrol.inc:4781
> #2 $00480c53 in TWINCONTROL__CREATEHANDLE (this=$2216928)
> at wincontrol.inc:4723
> #3 $004818ac in TWINCONTROL__HANDLENEEDED (this=$2216928)
> at wincontrol.inc:5031
> #4 $0047ff73 in TWINCONTROL__GETHANDLE (this=$2216928) at
> wincontrol.inc:4073
> #5 $00482aa5 in TWINCONTROL__GETDEVICECONTEXT (WINDOWHANDLE=0,
> this=$2216928)
> at wincontrol.inc:5502
> #6 $004788f0 in TCONTROLCANVAS__CREATEHANDLE (this=$2199934)
> at controlcanvas.inc:90
> #7 $004b8180 in TCANVAS__REQUIREDSTATE (REQSTATE=[CSHANDLEVALID],
> this=$2199934) at canvas.inc:1403
> #8 $004b7a30 in TCANVAS__MOVETO (X1=2, Y1=2, this=$2199934) at
> canvas.inc:1075
> #9 $007c12b1 in TSIMPLELINE__PAINT (this=$2216928) at SimpleLine.pas:49
> #10 $007c127d in TSIMPLELINE__RESIZE (this=$2216928) at SimpleLine.pas:44
> ---------------- /backtrace-------------------------
>
> ---------------------- unit/component------------------------
> unit SimpleLine;
> {$mode objfpc}{$H+}
> interface
> uses
> Windows, Messages, SysUtils, Classes, GraphType,Graphics, Controls,
> Forms, Dialogs,
> ExtCtrls, LResources;
>
> type
> TSimpleLine = class(TCustomPanel)
> private
> { Private declarations }
> protected
> { Protected declarations }
> public
> { Public declarations }
> constructor Create(AOwner: TComponent); override;
> procedure Paint; override;
> procedure Resize; override;
> published
> property OnResize;
> { Published declarations }
> end;
>
> procedure Register;
>
> implementation
>
> procedure Register;
> begin
> RegisterComponents('Misc',[TSimpleLine]);
> end;
>
> constructor TSimpleLine.Create(AOwner: TComponent);
> begin
> inherited;
> end;
>
> procedure TSimpleLine.Resize;
> begin
> inherited;
> paint();
> end;
Don't call paint in Resize. This will be done automatically.
>
> // --------- this is where it all starts -----------------------
> procedure TSimpleLine.paint() ;
> begin
> Canvas.Moveto(2,2);
> Canvas.Lineto(4,4);
> end;
>
> end.
Mattias
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