ado.net实现省市选择框

把连接字符串放到配置文件中
配置文件不能改名
1、添加一个app.config的文件                     //使用应用程序配置文件的好处是修改数据库时不用重新编译程序
 <connectionStrings>
    <add name="str" connectionString="Data Source=.\sqlexpress;Initial Catalog=DataManager;Integrated Security=True"/>
  </connectionStrings>
2、在项目中添加引用 System.configuration
3、添加命名控件using System.configuration
4、string connStr = ConfigurationManager.ConnectionStrings["str"].ConnectionString;

 

设已有数据库DBPromary 中有province表和city表

 

建一个辅助类Province

 

using System;using System.Collections.Generic;using System.Linq;using System.Text;namespace WindowsFormsApplication2{    class Province    {        public Province()        { }        public Province(int proId, string proName)        {            this.ProId = proId;            this.ProName = ProName;        }        public int ProId { get; set; }        public string ProName { get; set; }        public override string ToString()        {            return this.ProName;        }    }}

正文

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 WindowsFormsApplication2{    public partial class Form1 : Form    {        public Form1()        {            InitializeComponent();        }        //读取连接字符串        string connStr = ConfigurationManager.ConnectionStrings["str"].ToString();        private void Form1_Load(object sender, EventArgs e)        {                        using (SqlConnection conn = new SqlConnection(connStr))            {                string sql="select * from promary";                using (SqlCommand cmd = new SqlCommand(sql, conn))                {                    conn.Open();                    using (SqlDataReader dr = cmd.ExecuteReader())                    {                        while (dr.Read())                        {                            //把数据行，转换成Province对象                            Province p = new Province();                            p.ProName = dr["ProName"].ToString();                            p.ProId = Convert.ToInt32(dr["ProId"]);                            cboProvince.Items.Add(p);                                                    }                                           }                }            }            if (cboProvince.Items.Count > 0)            {                //设置第一项被选中                cboProvince.SelectedIndex = 0;            }                    }        private void cboVince_SelectedIndexChanged(object sender, EventArgs e)        {                        //清空下拉菜单            cboCity.Items.Clear();            if (cboProvince.SelectedItem != null)            {                Province p = cboProvince.SelectedItem as Province;                if (p != null)                {                    string sql = "select * from city where proId=" + p.ProId;                    using (SqlConnection conn = new SqlConnection(connStr))                    {                        using (SqlCommand cmd = new SqlCommand(sql, conn))                        {                            conn.Open();                            using (SqlDataReader dr = cmd.ExecuteReader())                            {                                                                while (dr.Read())                                {                                    cboCity.Items.Add(dr["cityName"]);                                }                            }                        }                    }                }            }        }    }}