直接貼代碼了：

            <ItemTemplate>
               <tr >
               <td>
               <asp:DropDownList ID="DListNewsIsShow" runat="server" AutoPostBack="true" OnSelectedIndexChanged="DListNewsIsShow_SelectedIndexChanged">
                  <asp:ListItem Value="1">是</asp:ListItem>
                  <asp:ListItem Value="0">否</asp:ListItem>
               </asp:DropDownList><asp:Label ID="LabId" runat="server" Visible="false" Text='<%# Eval("id") %>'></asp:Label>
               </td>
            </ItemTemplate>

...

        //遍歷Rpt中DListNewsIsShow的數據讀取
        protected void RptNew_ItemDataBound(object sender, RepeaterItemEventArgs e)
        {
            if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem || e.Item.ItemType == ListItemType.SelectedItem)
            {
                DataRowView rowv = (DataRowView)e.Item.DataItem;
                DropDownList DListNewsIsShow = (DropDownList)e.Item.FindControl("DListNewsIsShow");
                DListNewsIsShow.Items.FindByValue(rowv["isshow"].ToString()).Selected = true;
            }
        }
                
        //異步更新新聞是否顯示
        protected void DListNewsIsShow_SelectedIndexChanged(object sender, EventArgs e)
        {
            DropDownList DListFNewsIsShow = sender as DropDownList;
            RepeaterItem item = DListFNewsIsShow.Parent as RepeaterItem;  //轉為所在Item
            Label LabFId = item.FindControl("LabId") as Label;　　//查找

            NewsInfo newsInfoRpt = new NewsInfo();
            newsInfoRpt.Id = LabFId.Text.ToString();
            newsInfoRpt.IsShow = Convert.ToInt16(DListFNewsIsShow.SelectedValue.ToString());
            if(news.Update(newsInfoRpt,"1")<=0)
            {
                ScriptManager.RegisterStartupScript(UpDPanelRptNews, typeof(UpdatePanel), "JsAlert", "alert('對不起，更新失?。?')", true);
            }
        }