全国省市选择

省市选择练习题：

界面设计：

当选择省后相应的省里面的市从数据库中读出。

具体实现代码为：

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.Data.Sql;
using System.Configuration;

namespace 省市数据库
{
    public partial class 省市 : Form
    {
        public 省市()
        {
            InitializeComponent();
        }

        private void 省市_Load(object sender, EventArgs e)
        {
           // string strconn = @"Data Source=.SQLEXPRESS;AttachDbFilename=F:学习C#练习C#时的代码ado.net省市数据库SS.mdf;Integrated Security=True;User Instance=True";
            string strconn = ConfigurationManager.ConnectionStrings["SS"].ConnectionString;//从app.config文件中读取数据库连接字符串
            using (SqlConnection conn=new SqlConnection (strconn))
            {
                conn.Open();
                string selectYuju="select * from promary";
                using (SqlCommand cmd = new SqlCommand(selectYuju,conn))
                {
                    SqlDataReader dr = cmd.ExecuteReader();
                    while (dr.Read())
                    {
                       // string PromaryName = dr.GetString(dr.GetOrdinal("proName"));
                        ProItem item = new ProItem();//创建一个对象，对象中两个字段对应省的名字和省的ID
                        item.proName = dr.GetString(dr.GetOrdinal("proName"));
                        item.proID = dr.GetInt32(dr.GetOrdinal ("proID"));
                        cmd省.Items.Add(item);//将创建的对象添加到comboBox控件中，在这里需要修改一下该comboBox控件的一个属性，将
                        //属性中的DisplayMemeber设置为proName

                    }
                }
            }
        }
        private void cmd省_SelectedIndexChanged(object sender, EventArgs e)
        {
            cmd市.Items.Clear();
            ProItem selectedItem = (ProItem)cmd省.SelectedItem;
            int selectedproID=selectedItem.proID;
           // string strconn = @"Data Source=.SQLEXPRESS;AttachDbFilename=F:学习C#练习C#时的代码ado.net省市数据库SS.mdf;Integrated Security=True;User Instance=True";
            string strconn = ConfigurationManager.ConnectionStrings["SS"].ConnectionString;
            using (SqlConnection conn = new SqlConnection(strconn))
            {
                conn.Open();
                string selectYuJu = "select cityName from city where proID=@proid";
                using (SqlCommand cmd = new SqlCommand(selectYuJu, conn))
                {
                    cmd.Parameters.Add(new SqlParameter("proid", selectedproID));
                    SqlDataReader dr=cmd.ExecuteReader ();
                    while (dr.Read())
                    {
                        cmd市.Items.Add(dr.GetString (dr.GetOrdinal ("cityName")));
                    }
                }

            }
        }

        private void cmd市_SelectedIndexChanged(object sender, EventArgs e)
        {
            ProItem p1 = (ProItem)cmd省.SelectedItem;
            string sheng= p1.proName;
            string shi = (string)cmd市.SelectedItem;
            MessageBox.Show(sheng +shi );
        }
    
    }
    public class ProItem
    {
        public int proID { get; set; }
        public string proName { get; set; }
        
    }
}

配置文件中的代码为：

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings >
    <add name="SS" connectionString="Data Source=.SQLEXPRESS;AttachDbFilename=F:学习C#练习C#时的代码ado.net省市数据库SS.mdf;Integrated Security=True;User Instance=True"/>
  </connectionStrings>
  
</configuration>

运行结果为：