自建List<>绑定ComboBox下拉框实现省市联动

 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 _04省市联动
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

            //所有的省份显示到第一个下拉框中
            LoadAreaByAreaPid(0);//参数是列名AreaId的值

        }

        private void LoadAreaByAreaPid(int p)//参数p是列名AreaId的值
        {

            List<Area> list = new List<Area>();
            list.Add(new Area() { AreaId = -1, AreaName = "请选择" });
            string sql = "select AreaId,AreaName from TblArea where AreaPId=" + p;//参数p是列名AreaId的值
            using (SqlDataReader reader = SqlHelper.ExecuteReader(sql))
            {
                if (reader.HasRows)
                {
                    while (reader.Read())
                    {
                        Area a = new Area();
                        a.AreaId = Convert.ToInt32(reader["AreaId"]);
                        a.AreaName = reader["AreaName"].ToString();
                        list.Add(a);
                    }
                }
            }

            cmbSheng.DataSource = list;//绑定数据源
            cmbSheng.DisplayMember = "AreaName";//主要是设置下拉框显示的值
            cmbSheng.ValueMember = "AreaId";//实际值

        }

        private void cmbSheng_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (cmbSheng.SelectedIndex!=0)
            {

                cmbCheng.Items.Clear();//清空
                //获取当前选中的省份的id

                int id = Convert.ToInt32(cmbSheng.SelectedValue);
                string sql = "select AreaId,AreaName from TblArea where AreaPId=" + id;
                using (SqlDataReader reader = SqlHelper.ExecuteReader(sql))
                {
                    if (reader.HasRows)
                    {
                        while (reader.Read())//练习
                        {
                            Area a = new Area();
                            a.AreaId = Convert.ToInt32(reader["AreaId"]);
                            a.AreaName = reader["AreaName"].ToString();
                            cmbCheng.Items.Add(a);//自带集合，要重写ToString()方法

                        }
                    }
                }
            }

        }
    }
}