using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Windows.Forms;using System.Data.SqlClient;

namespace 省市数据递归加载到TreeView{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void button1_Click(object sender, EventArgs e)        {            ////1.把所有的省份及直辖市加载到TreeView的根节点上。            //List<Area> listProvince = GetSubItemByParentId(0);            //foreach (Area item in listProvince)            //{            //    treeView1.Nodes.Add(item.AreaName);            //}            //递归将省市加载到TreeView中            LoadDataToTree(treeView1.Nodes, 0);        }        //递归加载到TreeView        private void LoadDataToTree(TreeNodeCollection treeNodeCollection, int pid)        {            //1.根据指定的pid获取该城市下的子城市            List<Area> listCity = GetSubItemByParentId(pid);            //2.遍历将获取到的数据绑定到treeNodeCollection节点集合中            foreach (var item in listCity)            {                //返回刚刚增加的这个节点                TreeNode node = treeNodeCollection.Add(item.AreaName);                LoadDataToTree(node.Nodes, item.Areaid);            }        }        //先封装一个方法，根据父Id查询下面的所有子项        private List<Area> GetSubItemByParentId(int pid)        {            List<Area> list = new List<Area>();            string sql = "select * from TblArea where areaPid=@pid";            using (SqlDataReader reader = SqlHelper.ExecuteReader(sql, new SqlParameter("@pid", pid)))            {                if (reader.HasRows)                {                    while (reader.Read())                    {                        Area model = new Area();                        model.Areaid = reader.GetInt32(0);                        model.AreaName = reader.GetString(1);                        model.AreaPid = reader.GetInt32(2);                        list.Add(model);                        /////不要直接在这里递归，一定要先把数据获取到一个集合中，然后再递归                        /////否则会打开很多个连接。                    }                }            }            return list;        }    }    public class Area    {        public int Areaid { get; set; }        public string AreaName { get; set; }        public int AreaPid { get; set; }    }}