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; }     //} }