ASP DROPDOWN 三级联动最好用

      <asp:ScriptManager ID="ScriptManager1" runat="server" EnablePartialRendering="true">
                            </asp:ScriptManager>
                            <asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
                                <ContentTemplate>
                                    <asp:DropDownList ID="dpSheng" runat="server" Width="120px"
                                        AutoPostBack="true" OnSelectedIndexChanged="dpProvince_SelectedIndexChanged" />
                                    <asp:DropDownList ID="dpShi" runat="server" AutoPostBack="true" Width="120px"
                                        OnSelectedIndexChanged="dpCity_SelectedIndexChanged" />
                                    <asp:DropDownList ID="dpXian" runat="server" AutoPostBack="false" Width="120px"/>
                                    <asp:UpdateProgress ID="UpdateProgress1" runat="server">
                                        <ProgressTemplate>
                                            正在加载...
                                        </ProgressTemplate>
                                    </asp:UpdateProgress>
                                </ContentTemplate>
                                <%-- 异步回送防止整页刷新 --%>
                                <Triggers>
                                    <asp:AsyncPostBackTrigger ControlID="dpSheng" EventName="SelectedIndexChanged" />
                                    <asp:AsyncPostBackTrigger ControlID="dpShi" EventName="SelectedIndexChanged" />
                                </Triggers>
                            </asp:UpdatePanel>

 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            BindSheng();
            BindShi();
            BindXian();
        }
    }

    private void BindSheng()
    {
        //获取省数据
        dpSheng.DataSource = baseParameterBll.GetModelDataList("par_type=0 and  par_parent='0'");
        dpSheng.DataValueField = "par_id";
        dpSheng.DataTextField = "par_name";
        dpSheng.DataBind();

        dpSheng.Items.Insert(0, new ListItem("选择省份", "-"));
    }

    private void BindShi()
    {
        string sheng = dpSheng.SelectedValue;

        if (sheng != "-")
        {
            dpShi.DataSource = baseParameterBll.GetModelDataList("par_type=0 and  par_parent='" + sheng + "'");
            dpShi.DataValueField = "par_id";
            dpShi.DataTextField = "par_name";
            dpShi.DataBind();
        }

        dpShi.Items.Insert(0, new ListItem("选择市", "-"));
    }

    private void BindXian()
    {
        string shi = dpShi.SelectedValue;

        if (shi != "-")
        {
            dpXian.DataSource = baseParameterBll.GetModelDataList("par_type=0 and  par_parent='" + shi + "'");
            dpXian.DataValueField = "par_id";
            dpXian.DataTextField = "par_name";
            dpXian.DataBind();
        }

        dpXian.Items.Insert(0, new ListItem("选择区", "-"));
    }

    protected void dpProvince_SelectedIndexChanged(object sender, EventArgs e)
    {
        dpShi.Items.Clear();
        BindShi();

        dpXian.Items.Clear();
        BindXian();
    }

    protected void dpCity_SelectedIndexChanged(object sender, EventArgs e)
    {
        dpXian.Items.Clear();
        BindXian();
    }
}
}