C# comboBox實現省市兩級聯動（winform）

建立一個win form應用程式，拖兩comboBox控制項。資料庫見前一篇文章。

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
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();}
 private void Form1_Load(object sender, EventArgs e)
        {
            using (SqlConnection conn = new SqlConnection("server=.;database=DBPromary;user id=sa;password=123456"))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "select proName from promary";
                    using (SqlDataReader reader = cmd.ExecuteReader())
                    {
                        while (reader.Read())
                        {
                            string name = reader.GetString(reader.GetOrdinal("proName"));
                            cb1.Items.Add(name);
                        }
                    }
                }
            }
        }


private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            cb2.Items.Clear();
using (SqlConnection conn = new SqlConnection("server=.;database=DBPromary;user id=sa;password=123456"))
            {
                conn.Open();

using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = "select cityName from city,promary where city.proID=promary.proID and promary.proName=@pname";
                    cmd.Parameters.Add(new SqlParameter("pname",cb1.SelectedItem));

using (SqlDataReader reader = cmd.ExecuteReader())
                    {

while (reader.Read())
                        {
string name = reader.GetString(reader.GetOrdinal("cityName"));

                            cb2.Items.Add(name);
                        }
                    }
                }
            }

        }


        }
    }