Lazarus/Pascal: Problems with dynamic Toggleboxes - casting

Question

We have two classes which are important:
uSitz, uGUI.
unit uSitz;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, stdctrls;
type txyTogglebox=class(TTogglebox)
private
x:integer;
y:integer;
public
constructor create(xi,yi:integer;TheOwner:tobject);
end;
implementation
constructor txytogglebox.create(xi,yi:integer;TheOwner:tobject);
begin
x:=xi;
y:=yi;
end;
end.
It inherits the class TToggleBox!
So then we have the uGUI:
unit uGUI;
{$mode objfpc}{$H+}
interface
uses
Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs, usaal, usitz, stdctrls;
type
{ TForm1 }
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
private
{ private declarations }
public
{ public declarations }
end;
var
Form1: TForm1;
i,j:integer;
saal:tsaal;
xytoggles: array of array of txytogglebox;
implementation
{$R *.lfm}
{ TForm1 }
procedure toggleboxclick(Sender:TObject);
begin
end;
procedure TForm1.FormCreate(Sender: TObject);
begin
setlength(xytoggles, 10, 10);
saal.create(10,10);
for i:=0 to 10 do
begin
for j:=0 to 10 do
begin
xytoggles[i,j].create(i,j,form1);
xytoggles[i,j].parent:=form1;
xytoggles[i,j].Visible:=true;
xytoggles[i,j].top:=i*10;
xytoggles[i,j].left:=j*10;
xytoggles[i,j].width:=10;
xytoggles[i,j].height:=10;
xytoggles[i,j].onclick:=#toggleboxclick;
end;
end;
end;
end.
So the compiler says that we have an error #: ugui.pas(64,29) Error: Incompatible types: got "<address of procedure(TObject);Register>" expected "<procedure variable type of procedure(TObject) of object;Register> ".
If i change the procedure "toggleboxclick" to TForm1.toggleboxclick i will get a new error: nullpointer-exception (sigserv or something like this) # "xytoggles[i,j].parent:=form1;". How i can solve this problem.
At last: Sry for my english ;)

Answer 1

If i change the procedure "toggleboxclick" to TForm1.toggleboxclick
That is the correct way to do it
i will get a new error: nullpointer-exception (sigserv or something like this) # "xytoggles[i,j].parent:=form1;". How i can solve this problem.
You cannot use object.create. You need to use object := TClass.create. I.e.: In your case:
saal := tsaal.create(10, 10);
xytoggles[i,j] := txyTogglebox.create(i,j,form1);
It is also bad style to have global variables like i,j,saal, xytoggles. Better make i,j local variables; and saal, xytoggles class fields