三级联动

上一级选项变动，下一集选项也随之变动！

在窗体建立三个ComBox。

//数据类
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace WindowsFormsApplication3.App_Code
{
    public class China
    {
        private string _AreaCode;//地区的代码
        public string AreaCode
        {
            get { return _AreaCode; }
            set { _AreaCode = value; }
        }


        private string _AreaName;//地区的名字
        public string AreaName
        {
            get { return _AreaName; }
            set { _AreaName = value; }
        }


        private string _ParentAreaCode;//他的上一级地区的代码
        public string ParentAreaCode
        {
            get { return _ParentAreaCode; }
            set { _ParentAreaCode = value; }
        }


    }
}

//数据访问类
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.SqlClient;

namespace WindowsFormsApplication3.App_Code
{
    public class ChinaData
    {
        SqlConnection cnn = null;
        SqlCommand cmd = null;
        public ChinaData()
        {
            cnn = new SqlConnection("server=.;database=mydb;user=sa;pwd=123");
            cmd = cnn.CreateCommand();

        }
        public List<China> select(string code)
        {
            List<China> list = new List<China>();
            cmd.CommandText = "select * from ChinaStates where ParentAreaCode=@a";
            cmd.Parameters.Clear();
            cmd.Parameters.Add("@a",code);
            cnn.Open();
            SqlDataReader ss = cmd.ExecuteReader();
            while (ss.Read())
            {
                China c = new China();
                c.AreaCode = ss[0].ToString();
                c.AreaName = ss[1].ToString();
                c.ParentAreaCode = ss[2].ToString();
                list.Add(c);
            }
            cnn.Close();
            return list;
         }


    }
}

//form1里面
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using WindowsFormsApplication3.App_Code;

namespace WindowsFormsApplication3
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();

            dong(comboBox1, "0001");
            //comboBox1.DataSource = new ChinaData().select("0001");
            //comboBox1.ValueMember = "AreaCode";
            //comboBox1.DisplayMember = "AreaName";

            dong(comboBox2,comboBox1.SelectedValue.ToString());
            //comboBox2.DataSource = new ChinaData().select(comboBox1.SelectedValue.ToString());
            //comboBox2.ValueMember = "AreaCode";
            //comboBox2.DisplayMember = "AreaName";

            dong(comboBox3, comboBox2.SelectedValue.ToString());
            //comboBox3.DataSource = new ChinaData().select(comboBox2.SelectedValue.ToString());
            //comboBox3.ValueMember = "AreaCode";
            //comboBox3.DisplayMember = "AreaName";

        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }

        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            dong(comboBox2, comboBox1.SelectedValue.ToString());
            //comboBox2.DataSource = new ChinaData().select(comboBox1.SelectedValue.ToString());
            //comboBox2.ValueMember = "AreaCode";
            //comboBox2.DisplayMember = "AreaName";
        }

        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e)
        {
            dong(comboBox3, comboBox2.SelectedValue.ToString());
            //comboBox3.DataSource = new ChinaData().select(comboBox2.SelectedValue.ToString());
            //comboBox3.ValueMember = "AreaCode";
            //comboBox3.DisplayMember = "AreaName";
        }

        public void dong(ComboBox c, string code)
        {
            c.DataSource = new ChinaData().select(code);
            c.ValueMember = "AreaCode";
            c.DisplayMember = "AreaName";
        }
    }
}