protected void ChkGridViewColumnList_SelectedIndexChanged(object sender, EventArgs e)
{
    int _index = Convert.ToInt32(Request.Form["__EVENTTARGET"].Substring(Request.Form["__EVENTTARGET"].LastIndexOf("$") + 1));
    ListItem _this = this.ChkGridViewColumnList.Items[_index];
    Response.Write("当前选择项值"+_this.Value);
}