几个数据库的小案例（二）：极其简单的省市联动

总用有两个文件(frmMain.cs SqlHelper.cs)

//frmMain.cs
//作者：Me
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;

namespace 省市联动小案例
{
    public partial class frmMain : Form
    {
        public frmMain()
        {
            InitializeComponent();
        }

        //private void ClearAll()
        //{
        //    cbCity.Items.Clear();
        //    cbProvince.Items.Clear();
        //    cbTown.Items.Clear();
        //}
        
        private void Form1_Load(object sender, EventArgs e)
        {
            //调用Load，加载省
            SqlHelper.Load(cbProvince, 0);
        }

        private void cbProvince_SelectedIndexChanged(object sender, EventArgs e)
        {
            cbCity.Items.Clear();
            
            //调用GetAreaId，获取省的id
            int proId = SqlHelper.GetAreaId(cbProvince.SelectedItem.ToString());
            //调用Load，加载市
            SqlHelper.Load(cbCity, proId);

        }

        private void cbCity_SelectedIndexChanged(object sender, EventArgs e)
        {
            cbTown.Items.Clear();

            //调动GetAreaId，获得市的id
            int cityId = SqlHelper.GetAreaId(cbCity.SelectedItem.ToString());
            //调用Load方法，加载镇
            SqlHelper.Load(cbTown, cityId);

        }

        private void btnShow_Click(object sender, EventArgs e)
        {
            //MessageBox.Show(cbProvince.SelectedItem.ToString()+":"+cbCity.SelectedItem.ToString()+":"+cbTown.SelectedItem.ToString());
            string province = "";
            string city = "";
            string town = "";
            if (cbProvince.SelectedIndex != -1)
            {
                province = cbProvince.SelectedItem.ToString();
            }

            if (cbCity.SelectedIndex != -1)
            {
                city = ":" + cbCity.SelectedItem.ToString();
            }

            if (cbTown.SelectedIndex != -1)
            {
                town = ":" + cbTown.SelectedItem.ToString();
            }

            MessageBox.Show(province+city+town);
        }
    }
}

以下是SqlHelper.cs

//SqlHelper.cs
//作者：Me
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.SqlClient;
using System.Windows.Forms;

namespace 省市联动小案例
{
    class SqlHelper
    {
        //连接字符串
        private static string sqlStr = "server=.;database=WebSite;uid=sa;pwd=123456";

        /// <summary>
        /// 通过名称获取id
        /// </summary>
        /// <param name="province">名字</param>
        /// <returns>id</returns>
        public static int GetAreaId(string province)
        {
            using (SqlConnection conn = new SqlConnection(sqlStr))
            {
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    SqlDataReader dr = null;
                    cmd.CommandText = "select ar_id from Area where ar_name = @name";
                    cmd.Parameters.Add(new SqlParameter("@name", province));
                    try
                    {
                        conn.Open();
                        dr = cmd.ExecuteReader();
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show("数据库错误：
" + ex.Message);
                        return 0;
                    }

                    
                    dr.Read();

                    return dr.GetInt32(0);
                    
                }
            }
        }

        /// <summary>
        /// 通过id，加载名字
        /// </summary>
        /// <param name="cbCity">cbo控件</param>
        /// <param name="proId">id</param>
        public static void Load(ComboBox cbCity, int proId)
        {
            using (SqlConnection conn = new SqlConnection(sqlStr))
            {
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    SqlDataReader dr = null;
                    cmd.CommandText = "select ar_name from Area where ar_uid = @proId";
                    cmd.Parameters.Add(new SqlParameter("@proId", proId));
                    try
                    {
                        conn.Open();
                        dr = cmd.ExecuteReader();
                    }
                    catch (Exception ex)
                    {
                        MessageBox.Show("数据库错误：
" + ex.Message);
                        return;
                    }

                    if (dr.HasRows)
                    {
                        while (dr.Read())
                        {
                            cbCity.Items.Add(dr[0].ToString());
                        }
                    }
                }
            }
        }
        //End
    }
}

各种控件的命名和属性

控件名	属性	事件
cbProvince		cbProvince_SelectedIndexChanged
cbCity		cbCity_SelectedIndexChanged
cbTown
btnShow		btnShow_Click