<html xmlns="http://www.w3.org/1999/xhtml" ><head runat="server"> <title>无标题页</title> <script type="text/javascript" language="javascript"> function CheckSelect() 
{
//alert("123"); var tb=document.getElementById("CheckBoxList1"); for(var i=0;i<tb.rows.length;i++)
{
var chk = tb.rows[i].firstChild.firstChild; if(chk != event.srcElement) { chk.checked=false;
} }
} </script></head><body> <form id="form1" runat="server"> <div> <asp:CheckBoxList ID="CheckBoxList1" runat="server" AutoPostBack="True" onclick="CheckSelect()"> <asp:ListItem>First</asp:ListItem> <asp:ListItem>Second</asp:ListItem> <asp:ListItem>Three</asp:ListItem> </asp:CheckBoxList> </div> </form></body></html>如果不用JavaScript脚本，直接在后台代码实现也可以：
using System;using System.Data;using System.Configuration;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Web.UI.HtmlControls;public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { //先遍历CheckBoxList 取出只有1个选项时候的index int iCount=0;int iTemp=0; for (int i = 0; i < CheckBoxList1.Items.Count; i++) { if (CheckBoxList1.Items[i].Selected) { iCount++; iTemp=i; } } if (iCount == 1) { ViewState["oldSelect"] = iTemp; } } protected void CheckBoxList1_SelectedIndexChanged(object sender, EventArgs e) { if (!CheckBox1.Checked) { int iCount = 0; int iTemp = (Int32)ViewState["oldSelect"]; for (int i = 0; i < CheckBoxList1.Items.Count; i++) { if (CheckBoxList1.Items[i].Selected) { iCount++; if (i != iTemp) { ViewState["newSelect"] = i; } } } if (iCount > 1)//点下第二个 { int iTempOld = (Int32)ViewState["oldSelect"]; int iTempNew = (Int32)ViewState["newSelect"]; CheckBoxList1.Items[iTempOld].Selected = false; CheckBoxList1.Items[iTempNew].Selected = true; ViewState["oldSelect"] = ViewState["newSelect"]; } } }}
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