delphi - StringGrid Objects - access violation -

i trying make use of objects property of stringgrid inside descendant , think doing wrong. so, created simple class use in stringgrid cells, like:

type    tkind = (tknone,tkstart, tkend, tkmiddle);    tmycell = class(tobject)   private     fkind:string; // tkind: start, middle, end, none     foftype:string; // new, registered, paid, over, none     factualdate:tdate;      fthetext:string; // if want show text in     fisweekend:boolean;     function isitweekend(dt:tdate):boolean;     procedure setkind(s:string);     { private declarations }   protected     { protected declarations }   public     constructor create;     property kind:string read fkind write setkind;     property oftype:string read foftype write foftype;     property actualdate:tdate read factualdate write factualdate;     property thetext:string read fthetext write fthetext;     property isweekend:boolean read fisweekend write fisweekend default false;     { public declarations }   published     { published declarations }   end;   implementation  procedure tmycell.setkind(s:string); begin   fkind:=s; end;  function tmycell.isitweekend(dt:tdate):boolean; begin   if (dayoftheweek(dt)=6) or (dayoftheweek(dt)=7) isitweekend:=true else isitweekend:=false;     end;  constructor tmycell.create; var   i:integer;   a,l,z:word;   dt:tdate; begin   fkind:='none';   foftype:='none';   factualdate:=now;   fthetext:='';   fisweekend:=isitweekend(factualdate); end; 

then, in stringgrid descendant (tmygrid), following:

 tmygrid = class(tstringgrid)   private     fstartselection:integer;     ffixedcolor:tcolor;     frowcount:integer;   ...   published     property colcount;     property rowcount;   ...  constructor tmygrid.create(aowner: tcomponent); var   i:integer;   a,l,z:word;   dt:tdate;   j: integer;   mycell:tmycell; begin   inherited;   ...// different settings   rowcount:=5;   := 0 colcount-1     j := 0 rowcount-1       begin         objects[i, j] := tmycell.create;       end; end;  destructor tmygrid.destroy; var   i,j:integer; begin   := 0 colcount-1     j := 0 rowcount-1       begin         tmycell(objects[i, j]).free;       end;   inherited; end;  ... // other stuff  procedure register; begin   registercomponents('mygrid', [tmygrid]); end; 

the problem don't know how tell control there more rows when developer changes rowcount in objectinspector before running app. drop stringrid descendant on form, , set rowcount 10. stringgrid not have objects created new rows, cells on arow=5->9 not have objects created... because in oncreate set initial value of rowcount 5 , create objects i:=0 rowcount-1.

is there event or method can tell stringgrid create objects after developer changes rowcount in objectinspector?

i sure problem because, using above code, when drop stringgrid on form , set it's rowcount (design time or runtime) 10 want assign value kind property of cell on row>4 accessviolation, if row <= 4 assignment works fine.

i found should here: http://embarcadero.newsgroups.archived.at/public.delphi.ide/200904/0904193279.html not know how , place code in stringgrid descendant class called when rowcount changed @ designtime/runtime

edit

after reading comments tried idea (that seemed work) override sizechanged (i did not know method existed, must have skipped when serached before). anyway, added code class:

tmygrid = class(tstringgrid)   private     ...     procedure sizechanged(oldcolcount, oldrowcount: longint); override;     procedure updategriddimensions(newcolcount, newrowcount: integer);     ...  procedure tmygrid.sizechanged(oldcolcount, oldrowcount: longint); begin   inherited;   if (oldrowcount<>frowcount)or(oldcolcount<>colcount)     updategriddimensions(colcount, frowcount); end;   procedure tmygrid.updategriddimensions(newcolcount, newrowcount: integer);  var     c, r: integer;     old: integer;  begin     if newcolcount <> colcount     begin         if newcolcount < colcount         begin             r := 0 rowcount-1             begin                 c := colcount-1 downto newcolcount                     objects[c, r].free;             end;         end;          old := colcount;         colcount := newcolcount;          if newcolcount > old         begin             r := 0 rowcount-1             begin                 c := old newcolcount-1                     objects[c, r] := tmycell.create;             end;         end;     end;      if newrowcount <> rowcount     begin         if newrowcount < rowcount         begin             c := 0 colcount-1             begin                 r := rowcount-1 downto newrowcount                     objects[c, r].free;             end;         end;          old := rowcount;         rowcount := newcolcount;          if newrowcount > old       begin             c := 0 colcount-1             begin                 r := old newrowcount-1                     objects[c, r] := tmycell.create;             end;         end;     end;  end; 

but whenever drop control on form, rowcount 93... set rowcount? because dont.

and still, if increase rowcount 93 else 100, objects exist first 93 rows not created 93-100 rows...

so idea sounded great, not work expect it...

any thoughts? doing wrong?

// sizechanged - called when size of grid has changed. protected   procedure sizechanged(oldcolcount, oldrowcount: longint); dynamic; 

you can override dynamic method sizechanged , initialize grid according new size. can check designtime or not (lu rd suggested link). , david mentioned, better keep objects property consumers of component. create , use own tlist/tobjectlist instead.