C# winform combobox 在绑定数据之后插入一项选择项

 1        }

 ProductCatalogListBLL productCatalogListBLL = new ProductCatalogListBLL();
        /// <summary>
        /// 
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                BindClass();
            }
        }
        /// <summary>
        /// 
        /// </summary>
        void BindClass()
        {
            List<ProductCatalogListInfo> list = productCatalogListBLL.get_List();
            foreach (ProductCatalogListInfo model in list)
            {
                ListItem li = new ListItem();
                li.Text = "╋" + model.ProductCatalogName;
                li.Value = model.ProductCatalogId.ToString();
                DropDownList1.Items.Add(li);
                BindChild(model.ProductCatalogId.ToString(), "├──");
            }
        }
        /// <summary>
        /// 
        /// </summary>
        /// <param name="ParentID"></param>
        /// <param name="separator"></param>
        void BindChild(string ParentID, string separator)
        {
            List<ProductCatalogListInfo> list = productCatalogListBLL.get_List(ParentID);
            foreach (ProductCatalogListInfo model in list)
            {
                ListItem li = new ListItem();
                li.Text = separator + model.ProductCatalogName;
                li.Value = model.ProductCatalogId.ToString();
                DropDownList1.Items.Add(li);
                string separator_ = separator + "───";
                BindChild(model.ProductCatalogId.ToString(), separator_);
            }
        }

　　

 /// <summary>
        /// 
        /// </summary>
        /// <returns></returns>
        public List<ProductCatalogListInfo> get_List()
        {
            List<ProductCatalogListInfo> List = new List<ProductCatalogListInfo>();
            DataTable dt = DBHelper.getDataSet("select * from ProductCatalogList where ProductCatalogParent=0 order by ProductCatalogId desc").Tables[0];
            foreach (DataRow dr in dt.Rows)
            {
                ProductCatalogListInfo model = new ProductCatalogListInfo();
                model.ProductCatalogId = Convert.ToInt32(dr["ProductCatalogId"]);
                model.ProductCatalogName = dr["ProductCatalogName"].ToString();
                model.ProductCatalogParent = Convert.ToInt32(dr["ProductCatalogParent"]);
                List.Add(model);
            }
            return List;
        }
        /// <summary>
        /// 
        /// </summary>
        /// <param name="ParentID"></param>
        /// <returns></returns>
        public List<ProductCatalogListInfo> get_List(string ParentID)
        {
            List<ProductCatalogListInfo> List = new List<ProductCatalogListInfo>();
            DataTable dt = DBHelper.getDataSet("select * from ProductCatalogList where ProductCatalogParent=" + ParentID + " order by ProductCatalogId desc").Tables[0];
            foreach (DataRow dr in dt.Rows)
            {
                ProductCatalogListInfo model = new ProductCatalogListInfo();
                model.ProductCatalogId = Convert.ToInt32(dr["ProductCatalogId"]);
                model.ProductCatalogName = dr["ProductCatalogName"].ToString();
                model.ProductCatalogParent = Convert.ToInt32(dr["ProductCatalogParent"]);
                List.Add(model);
            }
            return List;
        }