Repeater checkbox 后台判断选中

 <asp:Repeater ID="GridView1" runat="server">
                            <HeaderTemplate>
                             <tr>
   <th scope="col">
                                     <input id="all" type="checkbox" name="all" onclick="check_all(this,'checkid');" />
                                 </th><th scope="col">订单号</th><th scope="col">下单日期</th><th scope="col">订单详情</th><th scope="col">销售等级</th><th scope="col">订单状态</th><th scope="col">&nbsp;</th>
  </tr>
                            </HeaderTemplate>
                            <ItemTemplate>
                              <tr>
   <td>
   <input id="checkbox" runat="server" type="checkbox" value="" />
                <input type="hidden" id="HiddenID" runat="server" value='<%# DataBinder.Eval(Container.DataItem, "id")%>' />

 for (int i = 0; i < GridView1.Items.Count; i++)
        {
            if (((System.Web.UI.HtmlControls.HtmlInputCheckBox)GridView1.Items[i].FindControl("checkbox")).Checked)
            {
                string sql = "update OrderBase set orderstate='已接收' where id=" + ((System.Web.UI.HtmlControls.HtmlInputHidden)GridView1.Items[i].FindControl("HiddenID")).Value;
                fun.GetFunction().ExecuteSql(sql);
            }
        }