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 省市联动{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        private void Form1_Load(object sender, EventArgs e)        {            //加载省份信息到第一个ComboBox            LoadProvince();            //设置两个下拉菜单的默认值为“请选择”            comboBox1.SelectedIndex = 0;            comboBox2.SelectedIndex = 0;        }        private void LoadProvince()        {            string sql = "select * from TblArea where AreaPid=0";            using (SqlDataReader reader = SqlHelper.ExecuteReader(sql))            {                if (reader.HasRows)                {                    while (reader.Read())                    {                        ProvinceItem item = new ProvinceItem();                        item.AreaId = reader.GetInt32(0);                        item.AreaName = reader.GetString(1);                        item.AreaPid = reader.GetInt32(2);                        comboBox1.Items.Add(item);                    }                }            }            //为ComboBox 增加一个“请选择”            ProvinceItem itemDefault = new ProvinceItem();            itemDefault.AreaId = -1;            itemDefault.AreaName = "请选择";            comboBox1.Items.Insert(0, itemDefault);        }        //下拉菜单的选择项改变事件        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)        {            //获取当前用户选择的项            if (comboBox1.SelectedIndex > 0)            {                //加载第二个下拉菜单，数据来源：根据第一个下拉菜单用户选择项的AreaId来查询该项的所有子项。(子项：指的就是当前选中省份的下的直接城市)                //获取当前选中项的id                ProvinceItem item = comboBox1.SelectedItem as ProvinceItem;                int areaId = item.AreaId;                LoadCity(areaId);            }        }        private void LoadCity(int areaId)        {            comboBox2.Items.Clear();            string sql = "select * from TblArea where areaPId=@aid";            using (SqlDataReader reader = SqlHelper.ExecuteReader(sql, new SqlParameter("@aid", areaId)))            {                if (reader.HasRows)                {                    while (reader.Read())                    {                        ProvinceItem item = new ProvinceItem();                        item.AreaId = reader.GetInt32(0);                        item.AreaName = reader.GetString(1);                        item.AreaPid = reader.GetInt32(2);                        comboBox2.Items.Add(item);                    }                }            }            //也加一个【请选择】            ProvinceItem itemDefault = new ProvinceItem();            itemDefault.AreaId = -1;            itemDefault.AreaName = "请选择";            comboBox2.Items.Insert(0, itemDefault);            comboBox2.SelectedIndex = 0;        }    }    public class ProvinceItem    {        public int AreaId { get; set; }        public string AreaName { get; set; }        public int AreaPid { get; set; }        public override string ToString()        {            return this.AreaName;        }    }}