jQuery Grid Plugin - jqGrid

Hello, I am trying to hide jqgrid before to show a Dialog, but I don't know what's wrong with my code.

The jqgrid is defined like this <div id="dv_hc"><table id="tb_lsthc"></table></div>

The dialog works, but the jqgrid does not hide

Here is:

    function() dialog{
    $('#tb_lsthc').setGridParam({hiddengrid: true});
    $('#tb_lsthc').setGridParam({
        url: "hc/listhc.php?idusr=" + idusr, page: 1}).trigger('reloadGrid');
    $('#dv_hc').dialog('open');

}

 Thanks....