Webbrowser问题，深受困扰，求指点迷津

[ROBINTTT]

小弟上周刚从VB转学Dephi，这两天研究webbrowser编程碰到一个奇怪的问题，深受困扰，希望大侠们指点迷津，万谢。以下模块是在XE2环境下调试的。
procedure HideTable(myweb:TWebBrowser);
var
i:integer;
mydoc:HtmlDocument;
myelm:IHTMLElementCollection;
mytab:HtmlTable;
begin
mydoc:=myweb.Document as htmldocument;
myelm:=mydoc.getElementsByTagName('table') as IHTMLElementCollection;
//用for循环报错--Access Violation at address 00000000
for i:=0 to myelm.length-1 do
begin
mytab:=myelm.item(i,varempty) as htmltable;
(mytab.style as ihtmlstyle).display:='none';
end;
//用以下语句逐条赋值没有报错
//mytab:=myelm.item(0,varempty) as htmltable;
//(mytab.style as ihtmlstyle).display:='none';
//mytab:=myelm.item(1,varempty) as htmltable;
//(mytab.style as ihtmlstyle).display:='none';
//mytab:=myelm.item(2,varempty) as htmltable;
//(mytab.style as ihtmlstyle).display:='none';
end;

[grjs2004]

很显然是myelm.length不对
mytab:=myelm.item(i,varempty) as htmltable;

[ROBINTTT]

感谢grjs2004的回复。只是为什么不对呢，是语法吗，不好意思刚转学Delphi。
我就算改成 for i:=0 to 2 do也不对啊

[ROBINTTT]

自力更生，换一种思路，这个问题以后再想。如下代码执行OK
procedure HideTable(myweb:TWebBrowser);
var
i:integer;
tables:olevariant;
begin
tables:=myweb.OleObject.Document.all.tags('table');
for i:=0 to tables.length-1 do
begin
myweb.OleObject.Document.all.tags('table').item(i).style.display:='none';
end;
end;