dropdownlist里实现树状结构

有时,dropdownlist里也需要和treeview里一样的上下级关系,比如部门之间就有一个上下级的关系,
在dropdownlist 里我是这样实现的(原创).

#region
        int i_1=0;
        private void inittree_1()
        {
            
            string str;
            str="select * from GG_BiLu_WenHuaType";

            DataSet ds=DataProvider.DatabaseHelper.Instance().ExecuteDataSet(str); //返回一个DATASET

            DataView dv=ds.Tables[0].DefaultView;
            dv.RowFilter="ParentIIDD is null";

//            ListItem item1=new ListItem("---请选择---","-1");
//            drp_type.Items.Insert(0,item1);
            foreach(DataRowView dr in dv)
            {
                
                ListItem item=new ListItem();
                item.Value=dr["IIDD"].ToString();
                item.Text=dr["XUNWEN_type"].ToString();
                                
                drp_type.Items.Insert(i_1,item);
                i_1++;
                InitChildNode_1(item.Value);
            }
            drp_type.Items.Insert(i_1,new ListItem("---请选择---","-1"));
            drp_type.SelectedIndex=i_1;
            ds=null;
        }

        private void InitChildNode_1(string parentID)
        {
            string str;
            
            str="select * from GG_BiLu_WenHuaType";
         DataSet ds=DataProvider.DatabaseHelper.Instance().ExecuteDataSet(str);

            DataView dv=ds.Tables[0].DefaultView;
            dv.RowFilter="ParentIIDD='"+parentID+"'";

            string space = string.Empty;
            for(int m=0;m<i_1;m++) 
                space += "&nbsp;&nbsp;&nbsp;&nbsp;";
            foreach(DataRowView dr in dv)
            {


                HttpContext context = HttpContext.Current;

                ListItem item=new ListItem();
                item.Value=dr["IIDD"].ToString();
                item.Text=context.Server.HtmlDecode(space+dr["XunWen_type"].ToString());
                drp_type.Items.Insert(i_1,item);
                i_1++;
                InitChildNode_1(item.Value);
            }
            i_1--;
        }
        #endregion