省市地区的三级联动，每变更一次所选地都需要提交，但是又不需要把整个页面提交，所以我们需要使用控件：UdataPanel。工具--AJAX扩展
还有ScriptManager，并要将其放在页面的最顶端。
DropDownList则需要放在UpdatePanel中：
HTML源：
<body> <form id="form1" runat="server"> <div> <asp:ScriptManager ID="ScriptManager1" runat="server"> </asp:ScriptManager> </div> <asp:UpdatePanel ID="UpdatePanel1" runat="server"> <ContentTemplate> <asp:DropDownList ID="ddl_sheng" runat="server" AutoPostBack="true" DataTextField="Name" DataValueField="ParentId" OnSelectedIndexChanged="ddl_sheng_SelectedIndexChanged"> </asp:DropDownList> <asp:DropDownList ID="ddl_shi" runat="server" AutoPostBack="true" DataTextField="Name" DataValueField="ParentId" OnSelectedIndexChanged="ddl_shi_SelectedIndexChanged"> </asp:DropDownList> <asp:DropDownList ID="ddl_diqu" runat="server" DataTextField="Name" DataValueField="ParentId" OnSelectedIndexChanged="ddl_diqu_SelectedIndexChanged"> </asp:DropDownList> </ContentTemplate> </asp:UpdatePanel> </form> </body>
需要注意的是，在DropDownList的标签中，必须把AutoPostBack的属性设置为 true，自动回发数据。
DataTextField="Name" DataValueField="ParentId"
则是用来绑定显示的Text以及值Value。
cs中的代码：
DiquDataContext diqu=new DiquDataContext();//外部定义LINQ方便使用 protected void Page_Load(object sender, EventArgs e) { //第一次加载时才会走这里，必须要有，否则每次改动选择值时加载都会显示第一次加载的数据 if (!IsPostBack) { getsheng(); getshi(); getdiqu(); } } /// <summary> /// 绑定省 /// </summary> public void getsheng()//省 { var va = diqu.Members.Where(m => (m.ParentId.ToString().Length == 2)); ddl_sheng.DataSource = va; ddl_sheng.DataTextField = "Name"; ddl_sheng.DataValueField = "ParentId"; ddl_sheng.DataBind(); } /// <summary> /// 绑定市 /// </summary> public void getshi()//市 { string ss = ddl_sheng.SelectedValue;//获取显示的省的值。 var sh = diqu.Members.Where(m => (m.ParentId.ToString().Length == 4) && (m.ParentId.ToString().Substring(0, 2) == ss)); ddl_shi.DataSource = sh; ddl_shi.DataTextField = "Name"; ddl_shi.DataValueField = "ParentId"; ddl_shi.DataBind(); } /// <summary> /// 绑定地区 /// </summary> public void getdiqu() { string ss = ddl_shi.SelectedValue;//获取显示的省的值。 var sh = diqu.Members.Where(m => (m.ParentId.ToString().Length == 6) && (m.ParentId.ToString().Substring(0, 4) == ss)); ddl_diqu.DataSource = sh; ddl_diqu.DataTextField = "Name"; ddl_diqu.DataValueField = "ParentId"; ddl_diqu.DataBind(); } protected void ddl_shi_SelectedIndexChanged(object sender, EventArgs e) { getdiqu(); } protected void ddl_sheng_SelectedIndexChanged(object sender, EventArgs e) { getshi(); getdiqu(); } protected void ddl_diqu_SelectedIndexChanged(object sender, EventArgs e) { }