asp.net给DropDownList添加ToolTip(title)属性

asp.net给DropDownList添加ToolTip(title)属性
    /// <summary>
    /// 为DropDownList的Item加title属性
    /// </summary>
    /// <param name="ddl">DropDownList</param>
    private void addTitle(DropDownList ddl)
    {
        foreach (ListItem item in ddl.Items)
        {
            item.Attributes.Add("title", item.Text);
        }
    }
<script language="javascript" type="text/javascript">
        function showdropitem()//给页面全部select加title属性
        {
            var el = document.getElementsByTagName("select");
            for(i=0;i<el.length;i++)
            {
                showitem(el[i]);
            }
        }
        function showitem(obj)//将就需要加title属性的select传进来
        {
            for(j=0;j<obj.options.length;j++)
            {
                obj.options[j].title = obj.options[j].text;
            }
        }
</script>