using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace WindowsFormsApplication2

{

    public class China

    {

        public string AreaCode { get; set; }

        public string AreaName { get; set; }

        public string ParentAreaCode { get; set; }

    }

}

using System;

using System.Collections.Generic;

using System.Data.SqlClient;

using System.Linq;

using System.Text;

namespace WindowsFormsApplication2

{

    public class ChinaData

    {

        SqlConnection conn = null;

        SqlCommand cmd = null;

        public ChinaData()

        {

            conn = new SqlConnection("server=.;database=mydb;user=sa;pwd=123");

            cmd = conn.CreateCommand();

        }

        public List<China> Select(string pcode)

        {

            List<China> clist = new List<China>();

            cmd.CommandText = "select *from ChinaStates where ParentAreaCode = '" + pcode + "'";

            conn.Open();

            SqlDataReader dr = cmd.ExecuteReader();

            if (dr.HasRows)

            {

                while (dr.Read())

                {

                    China c = new China();

                    c.AreaCode = dr[].ToString();

                    c.AreaName = dr[].ToString();

                    c.ParentAreaCode = dr[].ToString();

                    clist.Add(c);

                }

            }

            conn.Close();

            return clist;

        }

        public List<China> Select()

        {

            List<China> clist = new List<China>();

            cmd.CommandText = "select *from ChinaStates";

            conn.Open();

            SqlDataReader dr = cmd.ExecuteReader();

            if (dr.HasRows)

            {

                while (dr.Read())

                {

                    China c = new China();

                    c.AreaCode = dr[].ToString();

                    c.AreaName = dr[].ToString();

                    c.ParentAreaCode = dr[].ToString();

                    clist.Add(c);

                }

            }

            conn.Close();

            return clist;

        }

    }

}

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;

namespace WindowsFormsApplication2

{

    public partial class Form1 : Form

    {

        List<China> AllList = new List<China>();

        public Form1()

        {

            InitializeComponent();

            AllList = new ChinaData().Select();

            TreeNode tn1 = new TreeNode("中国");

            tn1.Tag = "";

            NodesBind(tn1);

            treeView1.Nodes.Add(tn1);

        }

        public void NodesBind(TreeNode tn)

        {

            //lambda 表达式

            List<China> clist = AllList.Where(r => r.ParentAreaCode == tn.Tag.ToString()).ToList();

            foreach (China c in clist)

            {

                TreeNode tnn = new TreeNode(c.AreaName);

                tnn.Tag = c.AreaCode;

                NodesBind(tnn);

                tn.Nodes.Add(tnn);

            }

        }

    }

}