获取不到点击checkbox后，它所关联的那个ID值

前台是这样的
 <ItemTemplate>
                                        <tr id="TableData">
                                            <td>
                                                <asp:CheckBox ID="chkItem" runat="server" />
                                            </td>
                                            <td>
                                                <asp:Label ID="lblID" Text='
                                   <%# DataBinder.Eval(Container.DataItem, "ID")%>' runat="server" Visible="false"></asp:Label>
                                            </td>
后台是：
 int i = 0;
            string ID = "";
            for (i = 0; i < this.rpt_Schedule.Items.Count; i++)
            {
                CheckBox cbox = (CheckBox)this.rpt_Schedule.Items[i].FindControl("chkItem");
                if (cbox.Checked == true)
                {
                    if (ID == "")
                    {
                        ID = "" + ((Label)this.rpt_Schedule.Items[i].FindControl("lblID")).Text + "";
                    }
为什么当选中了checkbox之后，他还是显示的没有选中，checked还是false？