ASP.NET实现省市区三级联动（局部刷新）

<asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>
    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
        <ContentTemplate>
            <asp:DropDownList ID="ddl_Province" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddl_Province_SelectedIndexChanged">
            </asp:DropDownList>
            <asp:DropDownList ID="ddl_City" runat="server" AutoPostBack="True" OnSelectedIndexChanged="ddl_City_SelectedIndexChanged">
            </asp:DropDownList>
            <asp:DropDownList ID="ddl_Area" runat="server">
            </asp:DropDownList>
        </ContentTemplate>
    </asp:UpdatePanel>

protected void Page_Load(object sender, EventArgs e)
        {
            if (!Page.IsPostBack)
            {
                BindProvince();
                BindCity(ddl_Province.SelectedItem.Value);
                BindArea(ddl_City.SelectedItem.Value);
            }
        }

        #region 三级省市区联动xml
        private void BindProvince()
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(Server.MapPath("ChinaArea.xml"));
            XmlNodeList nodelist = xmlDoc.SelectNodes("area/province[@provinceID]");
            ListItem li = null;
            foreach (XmlNode myNode in nodelist)
            {
                li = new ListItem();
                li.Value = myNode.Attributes["provinceID"].Value;
                li.Text = myNode.Attributes["province"].Value;
                this.ddl_Province.Items.Add(li);
            } 
        }
        private void BindCity(string code)
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(Server.MapPath("ChinaArea.xml"));
            XmlNodeList nodelist = xmlDoc.SelectNodes(string.Format("area/province[@provinceID={0}]/City",code)); 
            ListItem li = null;
            foreach (XmlNode myNode in nodelist)
            {
                li = new ListItem();
                li.Value = myNode.Attributes["CityID"].Value;
                li.Text = myNode.Attributes["City"].Value;
                this.ddl_City.Items.Add(li);
            } 
        }

        private void BindArea(string code)
        {
            XmlDocument xmlDoc = new XmlDocument();
            xmlDoc.Load(Server.MapPath("ChinaArea.xml"));
            XmlNodeList nodelist = xmlDoc.SelectNodes(string.Format("area/province/City[@CityID={0}]/Piecearea",code));
            ListItem li = null;
            foreach (XmlNode myNode in nodelist)
            {
                li = new ListItem();
                li.Value = myNode.Attributes["PieceareaID"].Value;
                li.Text = myNode.Attributes["Piecearea"].Value;
                this.ddl_Area.Items.Add(li);
            } 
        }

        protected void ddl_City_SelectedIndexChanged(object sender, EventArgs e)
        {
            ddl_Area.Items.Clear();
            BindArea(ddl_City.SelectedItem.Value);
        }

        protected void ddl_Province_SelectedIndexChanged(object sender, EventArgs e)
        {
            ddl_City.Items.Clear();
            ddl_Area.Items.Clear();
            BindCity(ddl_Province.SelectedItem.Value);
            BindArea(ddl_City.SelectedItem.Value);
        }
        #endregion