delphi+AO,无法获取Feature的问题,急

procedure TForm1.Button1Click(Sender: TObject);
var
im: imap;
lay: Ilayer;
lyr:IFeatureLayer;
ftrcls:IFeatureClass;
ftr:IFeature;
i: integer;
begin

im := mapc.Map;// 从MapControl取得接口
im.Get_Layer(0,lay);
lyr := lay as IFeatureLayer;

lyr.Get_FeatureClass(ftrcls);

ftrcls.FeatureCount(nil,i);
showmessage('Feature count:'+inttostr(i));// 这里正确显示Feature数量

//----------------------------------------------
<FONT color=#ff0000>if ftrcls.GetFeature(0,ftr)=s_false then // 这里方法返回s_ok,但ftr死活返回nil，就是取不到Feature</FONT>
showmessage('fail');

....

end;

同样的代码,用VB就没有问题,可以取到IFeature.

请高手帮忙看一下是怎么回事,谢谢.