ComboBox三级关联

<ext:ScriptManager ID="ScriptManager1" runat="server">
        <Listeners>
            <DocumentReady Handler="#{ProvinceStore}.load();" />
        </Listeners>
    </ext:ScriptManager>
    <ext:Store runat="server" ID="ProvinceStore">
        <Proxy>
            <ext:HttpProxy Method="POST" Url="../WebService/GetProvince.asmx/GetProvicesByRegion" />
        </Proxy>
        <Reader>
            <ext:XmlReader Record="Province">
                <Fields>
                    <ext:RecordField Name="ProvinceID" Type="String" Mapping="ProvinceID" />
                    <ext:RecordField Name="ProvinceName" Type="String" Mapping="ProvinceName" />
                </Fields>
            </ext:XmlReader>
        </Reader>
        <BaseParams>
            <ext:Parameter Name="regionName" Value="#{cmbRegion}.getValue()" Mode="Raw" />
        </BaseParams>
        <Listeners>
            <%--<Load Handler="#{cmbProvince}.setValue(#{cmbProvince}.store.getAt(0).get('ProvinceID'));" />--%>
        </Listeners>
    </ext:Store>
    <ext:Store runat="server" ID="CityStore">
        <Proxy>
            <ext:HttpProxy Method="POST" Url="../WebService/GetCity.asmx/GetCityByProvinceId" />
        </Proxy>
        <Reader>
            <ext:XmlReader Record="City">
                <Fields>
                    <ext:RecordField Name="CityId" Type="String" Mapping="CityId" />
                    <ext:RecordField Name="CityName" Type="String" Mapping="CityName" />
                </Fields>
            </ext:XmlReader>
        </Reader>
        <BaseParams>
            <ext:Parameter Name="provinceId" Value="#{cmbProvince}.getValue()" Mode="Raw" />
        </BaseParams>
        <Listeners>
            <%--<Load Handler="#{CityStore}.setValue(#{CityStore}.store.getAt(0).get('CityId'));" />--%>
        </Listeners>
    </ext:Store>
    <ext:Store runat="server" ID="DistrictStore">
        <Proxy>
            <ext:HttpProxy Method="POST" Url="../WebService/GetDistrict.asmx/GetDistrictByCityId" />
        </Proxy>
        <Reader>
            <ext:XmlReader Record="District">
                <Fields>
                    <ext:RecordField Name="DistrictID" Type="String" Mapping="DistrictID" />
                    <ext:RecordField Name="DistrictName" Type="String" Mapping="DistrictName" />
                </Fields>
            </ext:XmlReader>
        </Reader>
        <BaseParams>
            <ext:Parameter Name="CityID" Value="#{cmbCity}.getValue()" Mode="Raw" />
        </BaseParams>
        <Listeners>
            <%--<Load Handler="#{CityStore}.setValue(#{CityStore}.store.getAt(0).get('CityId'));" />--%>
        </Listeners>
    </ext:Store>

<ext:ComboBox ID="cmbCity" runat="server" FieldLabel="城市" EmptyText="Loading..."
                                                Editable="false" TypeAhead="true" Mode="Local" StoreID="CityStore" ForceSelection="true"
                                                TriggerAction="All" DisplayField="CityName" ValueField="CityId" ValueNotFoundText="Loading...">
                                                <Listeners>
                                                    <Select Handler="#{cmbDistrict}.clearValue();#{DistrictStore}.load();" />
                                                </Listeners>
                                            </ext:ComboBox>
<ext:ComboBox ID="cmbDistrict" runat="server" FieldLabel="区/县" StoreID="DistrictStore"
                                                EmptyText="Loading..." Editable="false" TypeAhead="true" Mode="Local" SelectOnFocus="true"
                                                ForceSelection="true" TriggerAction="All" DisplayField="DistrictName" ValueField="DistrictID"
                                                ValueNotFoundText="Loading...">
                                                 <Listeners >
                                                    <Select  Handler="#{txtAddress}.setValue(#{cmbProvince}.getText()+#{cmbCity}.getText()+#{cmbDistrict}.getText());" />
                                                </Listeners>
                                            </ext:ComboBox>
<ext:ComboBox ID="cmbRegion" runat="server" FieldLabel="区域" Editable="false" TypeAhead="true"
                                                Mode="Local" ForceSelection="true" TriggerAction="All" SelectOnFocus="true" EmptyText="Select a Region">
                                                <SelectedItem Value="华南地区" />
                                                <Listeners>
                                                    <Select Handler="#{cmbProvince}.clearValue();#{cmbCity}.clearValue();#{cmbDistrict}.clearValue();#{ProvinceStore}.load();" />
                                                </Listeners>
                                                <Items>
                                                    <ext:ListItem Text="华东地区" Value="华东地区" />
                                                    <ext:ListItem Text="华北地区" Value="华北地区" />
                                                    <ext:ListItem Text="东北地区" Value="东北地区" />
                                                    <ext:ListItem Text="华中地区" Value="华中地区" />
                                                    <ext:ListItem Text="华南地区" Value="华南地区" />
                                                    <ext:ListItem Text="西南地区" Value="西南地区" />
                                                    <ext:ListItem Text="西北地区" Value="西北地区" />
                                                    <ext:ListItem Text="港澳台" Value="港澳台" />
                                                </Items>
                                            </ext:ComboBox>
 <ext:ComboBox ID="cmbProvince" runat="server" StoreID="ProvinceStore" EmptyText="Loading..."
                                                Editable="false" TypeAhead="true" Mode="Local" SelectOnFocus="true" ForceSelection="true"
                                                TriggerAction="All" DisplayField="ProvinceName" ValueField="ProvinceID" ValueNotFoundText="Loading..."
                                                FieldLabel="省份">
                                                <Listeners>
                                                    <Select Handler="#{cmbCity}.clearValue();#{cmbDistrict}.clearValue();#{CityStore}.load();" />
                                                </Listeners>
                                            </ext:ComboBox>

public class GetProvince : System.Web.Services.WebService
{
    [WebMethod]
    public List<Province> GetProvicesByRegion(string regionName)
    {
        switch (regionName)
        {
            case null:
                return null;
            default:
                {
                    var ds =
                        Utilities.GetDsByTableName("select ProvinceID,ProvinceName from S_Province where Region='" +
                                                   regionName +
                                                   "' order by ProvinceID");
                    return (from DataRow dr in ds.Tables[0].Rows
                            select new Province(dr["ProvinceID"].ToString(), dr["ProvinceName"].ToString())).ToList();
                }
        }
    }

    public class Province
    {
        public Province()
        {

        }
        public Province(string provinceId, string provinceName)
        {
            ProvinceID = provinceId;
            ProvinceName = provinceName;
        }
        public string ProvinceID { get; set; }
        public string ProvinceName { get; set; }
    }
}