using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace 三级联动.Model{    class China    {        private string code;        public string Code        {            get { return code; }            set { code = value; }        }        private string name;        public string Name        {            get { return name; }            set { name = value; }        }        private string parentcode;        public string Parentcode        {            get { return parentcode; }            set { parentcode = value; }        }    }}

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Data.SqlClient;namespace 三级联动.DataConnection{    class DataConnection    {        private static string connstr="server=.; database=mydb; user=sa; pwd=ray;";        public static SqlConnection Conn        {            get{
    return new SqlConnection(connstr); }        }    }}

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Data.SqlClient;namespace 三级联动.DataOperation{    class ChinaData    {        private SqlConnection _conn;        private SqlCommand _cmd;        private SqlDataReader _dr;        public ChinaData()        {            _conn = DataConnection.DataConnection.Conn;            _cmd = _conn.CreateCommand();        }        //根据父级代号返回地区信息        public List
      
        Select(string pcode)        {            _cmd.CommandText = "select *from ChinaStates where ParentAreaCode=@pcode";            _cmd.Parameters.Clear();            _cmd.Parameters.AddWithValue("@pcode",pcode);            _conn.Open();            _dr = _cmd.ExecuteReader();            List
       
         list = new List
        
         ();            if (_dr.HasRows)            {                while (_dr.Read())                {                    Model.China data = new Model.China();                    data.Code = _dr[0].ToString();                    data.Name = _dr[1].ToString();                    data.Parentcode = _dr[2].ToString();                    list.Add(data);                }            }            _conn.Close();            return list;        }    }}
        
       
      

可视化界面操作：

后台代码：

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 三级联动{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        DataOperation.ChinaData cda = new DataOperation.ChinaData();        //填充省的方法        public void FillSheng()        {            List
     
       list = cda.Select("0001");            cmbSheng.DataSource = list;            cmbSheng.DisplayMember = "Name";            cmbSheng.ValueMember = "Code";        }        //填充市的方法        public void FillShi()        {            List
      
        list = cda.Select(cmbSheng.SelectedValue.ToString());            cmbShi.DataSource = list;            cmbShi.DisplayMember = "Name";            cmbShi.ValueMember = "Code";        }        //填充区的方法        public void FillQu()        {            List
       
         list = cda.Select(cmbShi.SelectedValue.ToString());            cmbQu.DataSource = list;            cmbQu.DisplayMember = "Name";            cmbQu.ValueMember = "Code";        }        //页面一加载运行三个方法        private void Form1_Load(object sender, EventArgs e)        {            FillSheng();            FillShi();            FillQu();        }        //填充市的下拉列表        private void cmbSheng_SelectionChangeCommitted(object sender, EventArgs e)        {            FillShi();            FillQu();        }        //填充区的下拉列表        private void cmbShi_SelectionChangeCommitted(object sender, EventArgs e)        {            FillQu();        }    }}