WPF 中combobox 二级 关系怎么搞？？


后台代码：

        /// <summary>
        /// 加载下拉框
        /// </summary>
        public void LoadCB_name()     --------------------------------------------------------------------------->第一个下拉框的加载
        {
            string strCB_name = "select CompanyName from Company";
           
            using (SqlConnection con = new SqlConnection(sql_conn))
            {
                con.Open();
                SqlCommand cmd = new SqlCommand(strCB_name,con);

                SqlDataAdapter sda = new SqlDataAdapter(cmd);
                DataTable dt = new DataTable();
                sda.Fill(dt);
           
                this.cb_Name.ItemsSource = dt.AsDataView();
                this.cb_Name.DisplayMemberPath = "CompanyName";
            }  
        }

       public void LoadCB_id()        -----------------------------------------------------------------> 第二个下拉款，根据第一个的选择，
                                                                                                                                                     显示下拉内容
        {
            string strCB_id = string.Format("select GoodsID from GoodsInfo where GoodsInfo.CompanyID=(select CompanyID  from Company  where CompanyName='{0}')", cb_Name.Text);

            using (SqlConnection con =&nb