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 省市聯動 
{ 
    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"));  //這里要特別注意數據庫字段的類型 proID在數據庫里是int型 
                            pr.proName = dr.GetString(dr.GetOrdinal("proName")); 
                            comboBox1.Items.Add(pr);//pr是一個Province對象。Province有一個proName和proID屬性。我將一個對象填充到comboBox1里。再讓comboBox1的DisplayMember屬性設置proName?！疽簿褪亲宑omboBox1顯示pr對象的proName屬性】。這樣在填充市級城市的時候我就可以找到當前選擇項comboBox1.SelectedItem（或者當前選擇對象）所對應的proID 
                        } 
                    } 
                } 
                comboBox1.SelectedIndex = 0;  //將comcomboBox1的默認選項設為0 
            } 
        } 
 
        private void comboBox2_SelectedIndexChanged(object sender, EventArgs e) 
        { 
        } 
 
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e) 
        { 
            comboBox2.Items.Clear(); //在選擇的時候先清空一下combox1里面的所以項，以免在更換省名的時候，與先前對應的省名下的市沒有刪除。 
            Province tem = (Province)comboBox1.SelectedItem; // 因為在comboBox1.Items.Add(pr)里添加的是對象。所以在這里講comBox1所選中的當前對象賦給tem對象 （tem對象下面有兩個屬性 proName和proID） 
             
            int id = tem.proID;  //將當前選中對象的的proID賦值給id，給下面的sql查詢語句使用 
            Tsql.GetConnection();// 獲取數據庫連接字符串。 
            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; //將comcomboBox1的默認選項設為0 
            } 
        } 
    } 
    class Tsql 
    { 
        public static string GetConnection() //數據庫連接字符串 
        { 
            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 省市選擇2
{
    public partial class Form1 : Form
    {
        publicForm1()
        {
            InitializeComponent();
        }
        privatevoid Form1_Load(objectsender,EventArgs e)
        {
            /*
            //測試代碼：執行這段代碼的情況下是可以吧 tom這個值添加到 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();
                            //將comboBox1控件的DisplayMember屬性設置為“ProvinceName”用來在comboBox1控件中顯示ProvinceName屬性的值
                           comboBox1.DisplayMember = "ProvinceName";
                            pv.ProvinceName =reader.GetString(reader.GetOrdinal("proName"));
                            pv.ProvinceID =reader.GetInt32(reader.GetOrdinal("proID"));
                            //雖然pv屬于對象，把一個對象添加到ComboxBox1中，控件顯示的值為對象的類名，但是在前面comboBox1.DisplayMember ="ProvinceName"處已經設置好控件要顯示的為 Province類的ProvinceName值，所以添加進去的是pv對象的ProvinceName值
                            comboBox1.Items.Add(pv);
                        }                     
                    }
                }
            }
        }
 
        privatevoid comboBox1_SelectedIndexChanged(object sender,EventArgse)       //注意這里是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())
                    {
                        //查詢city（市）表里的 proID與promary（省）表里proID相同的所有數據。
                        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("錯誤信息：" + 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; }
    //}
}