About Jquery Tab ui.index

About Jquery Tab ui.index

Hi,
I bind function in tabsshow as in
$('#tabs > ul').tabs().bind('tabsshow', function(event, ui) {
                   alert(ui.index);
}};
why ui.index is always undefined?
I tried to solve this but although spent a lot of hours still cannot solve T_T
Any idea?
Thanks a lot.<br clear="all">
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Best Regards,
N3T