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; 
using System.Configuration; 
 
namespace 省市联动 
{ 
    public partial class Form1 : Form 
    { 
        public Form1() 
        { 
            InitializeComponent(); 
        } 
 
        private void Form1_Load(object sender, EventArgs e) 
        { 
            Tsql.GetConnection(); 
            using (SqlConnection conn = new SqlConnection(Tsql.GetConnection())) 
            { 
                conn.Open(); 
                using (SqlCommand cmd = conn.CreateCommand()) 
                { 
                    cmd.CommandText = "select * from promary"; 
                    using (SqlDataReader dr = cmd.ExecuteReader()) 
                    { 
                        while (dr.Read()) 
                        { 
                            Province pr = new Province(); 
                            pr.proID = dr.GetInt32(dr.GetOrdinal("proID"));  //这里要特别注意数据库字段的类型 proID在数据库里是int型 
                            pr.proName = dr.GetString(dr.GetOrdinal("proName")); 
                            comboBox1.Items.Add(pr);//pr是一个Province对象。Province有一个proName和proID属性。我将一个对象填充到comboBox1里。再让comboBox1的DisplayMember属性设置proName。【也就是让comboBox1显示pr对象的proName属性】。这样在填充市级城市的时候我就可以找到当前选择项comboBox1.SelectedItem（或者当前选择对象）所对应的proID 
                        } 
                    } 
                } 
                comboBox1.SelectedIndex = 0;  //将comcomboBox1的默认选项设为0 
            } 
        } 
 
        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e) 
        { 
        } 
 
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e) 
        { 
            comboBox2.Items.Clear(); //在选择的时候先清空一下combox1里面的所以项，以免在更换省名的时候，与先前对应的省名下的市没有删除。 
            Province tem = (Province)comboBox1.SelectedItem; // 因为在comboBox1.Items.Add(pr)里添加的是对象。所以在这里讲comBox1所选中的当前对象赋给tem对象 （tem对象下面有两个属性 proName和proID） 
             
            int id = tem.proID;  //将当前选中对象的的proID赋值给id，给下面的sql查询语句使用 
            Tsql.GetConnection();// 获取数据库连接字符串。 
            using (SqlConnection conn = new SqlConnection(Tsql.GetConnection())) 
            { 
                conn.Open(); 
                using (SqlCommand cmd = conn.CreateCommand()) 
                { 
                     
                    cmd.CommandText = "select * from city where proID=@id"; 
                    cmd.Parameters.Add(new SqlParameter("id", id)); 
                    using (SqlDataReader dr = cmd.ExecuteReader()) 
                    { 
                        while (dr.Read()) 
                        { 
                            comboBox2.Items.Add(dr.GetString(dr.GetOrdinal("cityName"))); 
                        } 
                    } 
                } 
                comboBox2.SelectedIndex = 0; //将comcomboBox1的默认选项设为0 
            } 
        } 
    } 
    class Tsql 
    { 
        public static string GetConnection() //数据库连接字符串 
        { 
            string getConn = ConfigurationManager.ConnectionStrings["getConn"].ConnectionString; 
            return getConn; 
        }        
    } 
    class Province 
    { 
        public string proName { get; set; } 
        public int proID { get; set; } 
    } 
}

using System.Data.SqlClient;
namespace 省市选择2
{
    public partial class Form1 : Form
    {
        publicForm1()
        {
            InitializeComponent();
        }
        privatevoid Form1_Load(objectsender,EventArgs e)
        {
            /*
            //测试代码：执行这段代码的情况下是可以吧 tom这个值添加到 comboBox1中的。
            People p1 = new People();
            p1.name = "tom";
            p1.age = 25;
            comboBox1.Items.Add(p1.name);
            */
            using(SqlConnection conn =newSqlConnection("Data source=凡斌-VAIO;Initialcatalog=DBPromary;integrated security=true"))
            {
                conn.Open();
                using(SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "select * from promary";
                    using(SqlDataReader reader = cmd.ExecuteReader())
                    {
                        while (reader.Read())
                        {
                            //string str =reader.GetString(reader.GetOrdinal("proName"));
                            //comboBox1.Items.Add(str);
                            Province  pv =new  Province();
                            //将comboBox1控件的DisplayMember属性设置为“ProvinceName”用来在comboBox1控件中显示ProvinceName属性的值
                           comboBox1.DisplayMember = "ProvinceName";
                            pv.ProvinceName =reader.GetString(reader.GetOrdinal("proName"));
                            pv.ProvinceID =reader.GetInt32(reader.GetOrdinal("proID"));
                            //虽然pv属于对象，把一个对象添加到ComboxBox1中，控件显示的值为对象的类名，但是在前面comboBox1.DisplayMember ="ProvinceName"处已经设置好控件要显示的为 Province类的ProvinceName值，所以添加进去的是pv对象的ProvinceName值
                            comboBox1.Items.Add(pv);
                        }                     
                    }
                }
            }
        }
 
        privatevoid comboBox1_SelectedIndexChanged(object sender,EventArgse)       //注意这里是comboBox1不是comboBox2
        {
            try
            {
                Province  tem = (Province) comboBox1.SelectedItem;
                int id = tem.ProvinceID;
 
                comboBox2.Items.Clear();
                using(SqlConnection conn =newSqlConnection("Data source=凡斌-VAIO;Initialcatalog=DBPromary;integrated security=true"))
                {
                    conn.Open();
                    using (SqlCommand cmd = conn.CreateCommand())
                    {
                        //查询city（市）表里的 proID与promary（省）表里proID相同的所有数据。
                        cmd.CommandText = "select * from city where proID =@id";
                        cmd.Parameters.Add(new SqlParameter("id", id));
                        SqlDataReader dr = cmd.ExecuteReader();
 
                        while(dr.Read())
                        {
                           comboBox2.Items.Add(dr.GetString(dr.GetOrdinal("cityName")));
                        }
                    }
                }
            }
            catch(Exception ex)
            {
                MessageBox.Show("错误信息：" + ex.Message);
            }
        }
    }
  
    class Province
    {
        public string ProvinceName { get;set; }
        public int ProvinceID { get;set; }
    }
    //class People
    //{
    //   public string name { get; set; }
    //   public int age { get; set; }
    //}
}