Repeater1_ItemDataBound绑定的问题，为什么数据会下移

前台代码：
      <asp:Repeater ID="Repeater1" runat="server" OnItemDataBound="Repeater1_ItemDataBound"  OnItemCreated="Repeater1_ItemCreated">
              <ItemTemplate>
              
                <tr >
                  <td height="26" align="center" background=<%#imgpath %>>
                      <asp:HyperLink ID="HyperLink5" runat="server" NavigateUrl=<%#DataBinder.Eval(Container.DataItem, "id","index.aspx?classid={0}")%> CssClass=lfont20><%# DataBinder.Eval(Container.DataItem, "classname").ToString()%></asp:HyperLink>
                    
                    
                  </td>
                </tr>
                </ItemTemplate>
               </asp:Repeater>
后台CS代码：
    protected void Repeater1_ItemDataBound(object sender, RepeaterItemEventArgs e)
    {
        classid = Request.QueryString["classid"];
        if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem)
        {
            HyperLink hp = new HyperLink();
            hp = (HyperLink)e.Item.FindControl("HyperLink5");
            string quanbu = hp.NavigateUrl.ToString();
            int xx = hp.NavigateUrl.ToString().Length - 19;
            string panduan = quanbu.Substring(19, xx);
            if (panduan == classid)
            {
                imgpath = "rheology_images/images/rheology_04-02.gif";
            }
            else
            {
                imgpath = "rheology_images/images/rheology_04-03.gif";
            }
        }
    }我要的效果是：当我获得classid的值时，进行比较判断，从而改变前台的背景颜色，现在的问题：当我的CLASSID=1时，前台背景改变的是 panduan=2的背景，一次类推，当CLASSID=2是，改变的是panduan=3的背景，请问为什么