asp.net 国家,省,城市三级联动

下面代码当中,国家我设置的只是中国,当然也可以从数据里取出别的国家来.

        BinderToNationOrArea()绑定国家或地区,省份或洲,城市#region BinderToNationOrArea()绑定国家或地区,省份或洲,城市

        /**//// <summary>
        /// 绑定国家或地区
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void BinderToNationOrArea()
        ...{
            //打开数据库的连接
            if (cn.State == System.Data.ConnectionState.Closed)
                cn.Open();
            //国家或地区
            SqlCommand cmd = new SqlCommand("select * from NationArea where NationArea = '中国' ",cn);
            SqlDataReader sdr = cmd.ExecuteReader();
            this.ddlNationOrArea.DataSource = sdr;
            this.ddlNationOrArea.DataTextField = "NationArea";
            this.ddlNationOrArea.DataValueField = "NationAreaID";
            this.ddlNationOrArea.DataBind();
            sdr.Close();

            //省份或洲
            //得到国家的ＩＤ
            string NationAreaID = this.ddlNationOrArea.SelectedValue;

            cmd.CommandText = "select * from Province where NationAreaID = '" + NationAreaID + "'";
            sdr = cmd.ExecuteReader();
            this.ddlProvince.DataSource = sdr;
            this.ddlProvince.DataTextField = "ProvinceName";
            this.ddlProvince.DataValueField = "ProvinceID";
            this.ddlProvince.DataBind();
            sdr.Close();

            //城市
            //得到省的ＩＤ
            string ProvinceID = this.ddlProvince.SelectedValue;
            cmd.CommandText = "select * from City where ProvinceID = '" + ProvinceID + "'";
            sdr = cmd.ExecuteReader();
            this.ddlCity.DataSource = sdr;
            this.ddlCity.DataTextField = "CityName";
            this.ddlCity.DataValueField = "CityID";
            this.ddlCity.DataBind();
            sdr.Close();
            //关闭数据库的连接
            cn.Close();

            //本个控件的值
            //国家
            this.txtNationOrArea.Text = this.ddlNationOrArea.SelectedItem.Text.Trim();
            //省
            this.txtProvince.Text = this.ddlProvince.SelectedItem.Text.Trim();
            //市
            this.txtCity.Text = this.ddlCity.SelectedItem.Text.Trim();

            //显示邮政编码
            this.PostCode();
        }

    
        #endregion
        BinderToProvince()绑定各个省,或洲#region BinderToProvince()绑定各个省,或洲
    
        /**//// <summary>
        /// 绑定各个省,或洲
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void BinderToProvince()
        ...{
            if (cn.State == System.Data.ConnectionState.Closed)
                cn.Open();
            //省份或洲
            //得到国家的ＩＤ
            string NationAreaID = this.ddlNationOrArea.SelectedValue;

            SqlDataAdapter sda = new SqlDataAdapter("select * from Province where NationAreaID = '" + NationAreaID + "'",cn);
            DataSet ds = new DataSet();
            sda.Fill(ds,"Province");
            this.ddlProvince.DataSource = ds.Tables["Province"];
            this.ddlProvince.DataTextField = "ProvinceName";
            this.ddlProvince.DataValueField = "ProvinceID";
            this.ddlProvince.DataBind();

            //城市
            //得到省的ＩＤ
            string ProvinceID = this.ddlProvince.SelectedValue;
            sda.Fill(ds,"City");
            this.ddlCity.DataSource =ds.Tables["City"];
            this.ddlCity.DataTextField = "CityName";
            this.ddlCity.DataValueField = "CityID";
            this.ddlCity.DataBind();
            //关闭数据库的连接
            cn.Close();

            //省
            this.txtProvince.Text = this.ddlProvince.SelectedItem.Text.Trim();
            //城市
            this.txtCity.Text = this.ddlCity.SelectedItem.Text.Trim();

            //显示相应邮政编码
            this.PostCode();
        }

    
        #endregion
        BinderToCity() 绑定各个城市#region BinderToCity() 绑定各个城市
        /**//// <summary>
        /// 绑定各个城市
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void BinderToCity()
        ...{
            if (cn.State == System.Data.ConnectionState.Closed)
            cn.Open();
            //城市
            //得到省的ＩＤ
            string ProvinceID = this.ddlProvince.SelectedValue;
            
            SqlDataAdapter sda = new SqlDataAdapter("select * from City where ProvinceID = '" + ProvinceID + "'",cn);
            DataSet ds = new DataSet();
            sda.Fill(ds,"City");
            this.ddlCity.DataSource = ds.Tables["City"];
            this.ddlCity.DataTextField = "CityName";
            this.ddlCity.DataValueField = "CityID";
            this.ddlCity.DataBind();
            //关闭数据库的连接
            cn.Close();
            //省
            this.txtProvince.Text = this.ddlProvince.SelectedItem.Text.Trim();
            //市
            this.txtCity.Text = this.ddlCity.SelectedItem.Text.Trim();

            //显示相应的邮政编码
            this.PostCode();
        }
        #endregion