c#省市联动（sqlHelper的应用）

sqlHelper：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6 using System.Configuration;
 7 using System.Data.SqlClient;
 8
 9 namespace WindowsFormsApplication1
10 {
11     public class sqlHelper
12     {
13         private static readonly string str = ConfigurationManager.ConnectionStrings["conStr"].ConnectionString;
14         //增删改
15         public static int ExecuteNonquery(string sql, params SqlParameter[] ps)
16         {
17             using (SqlConnection con = new SqlConnection(str))
18             {
19                 using (SqlCommand cmd = new SqlCommand(sql, con))
20                 {
21                     con.Open();
22                     if (ps != null)
23                     {
24                         cmd.Parameters.AddRange(ps);
25                     }
26                     return cmd.ExecuteNonQuery();
27                 }
28             }
29
30         }
31         //首行首列
32         public static object ExecuteScalar(string sql, params SqlParameter[] ps)
33         {
34             using (SqlConnection con = new SqlConnection(str))
35             {
36                 using (SqlCommand cmd = new SqlCommand(sql, con))
37                 {
38                     con.Open();
39                     if (ps != null)
40                     {
41                         cmd.Parameters.AddRange(ps);
42                     }
43                     return cmd.ExecuteScalar();
44                 }
45             }
46         }
47         //查询
48         public static SqlDataReader ExecuteReader(string sql, params SqlParameter[] ps)
49         {
50             SqlConnection con = new SqlConnection(str);
51             using (SqlCommand cmd = new SqlCommand(sql, con))
52             {
53                 if (ps != null)
54                 {
55                     cmd.Parameters.AddRange(ps);
56                 }
57                 try
58                 {
59                     con.Open();
60                     return cmd.ExecuteReader(System.Data.CommandBehavior.CloseConnection);
61                 }
62                 catch (Exception ex)
63                 {
64                     con.Close();
65                     con.Dispose();
66                     throw ex;
67                 }
68             }
69         }
70     }
71 }

Form1设计：

Form1代码：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.ComponentModel;
 4 using System.Data;
 5 using System.Drawing;
 6 using System.Linq;
 7 using System.Text;
 8 using System.Threading.Tasks;
 9 using System.Windows.Forms;
10 using System.Data.SqlClient;
11
12 namespace WindowsFormsApplication1
13 {
14     public partial class Form1 : Form
15     {
16         public Form1()
17         {
18             InitializeComponent();
19         }
20
21         private void Form1_Load(object sender, EventArgs e)
22         {
23             LoadShengById2(0);
24         }
25
26         private void LoadShengById2(int p)
27         {
28             string sql = "select id1, name from city where id2=" + p;
29             List<City> list = new List<City>();
30             list.Add(new City() { Id1 = -1,Name = "请选择"});//加一个“请选择”，如果不加，点北京不出城市，为什么？
31             using (SqlDataReader reader = sqlHelper.ExecuteReader(sql))
32             {
33                 if (reader.HasRows)
34                 {
35                     while (reader.Read())
36                     {
37                         City c = new City();
38                         c.Id1 = Convert.ToInt32(reader["id1"]);
39                         c.Name = reader["name"].ToString();
40                         //c.Id2 = Convert.ToInt32(reader["id2"]);
41                         list.Add(c);
42                     }
43
44                 }
45             }
46             //下面的放在using外面
47             cobSheng.DataSource = list;
48             cobSheng.DisplayMember = "Name";//显示的是哪个名字的信息
49             cobSheng.ValueMember = "Id1";//实际保存的信息
50
51         }
52
53         private void cobSheng_SelectedIndexChanged(object sender, EventArgs e)
54         {
55             //一定要加判断，有选中才运行！
56             if (cobSheng.SelectedIndex != 0)
57             {
58                 //MessageBox.Show(cobSheng.SelectedValue.ToString());
59                 int id = Convert.ToInt32(cobSheng.SelectedValue);
60                 string sql = "select * from city where id2=" + id;
61                 List<City> list = new List<City>();
62                 using (SqlDataReader reader = sqlHelper.ExecuteReader(sql))
63                 {
64                     if (reader.HasRows)
65                     {
66                         while (reader.Read())
67                         {
68                             City c = new City();
69                             c.Id1 = Convert.ToInt32(reader["id1"]);
70                             c.Name = reader["name"].ToString();
71                             c.Id2 = Convert.ToInt32(reader["id2"]);
72                             list.Add(c);
73                         }
74                         cobShi.DataSource = list;
75                         cobShi.DisplayMember = "name";
76                     }
77                 }
78             }
79
80
81         }
82     }
83 }

City类：

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Linq;
 4 using System.Text;
 5 using System.Threading.Tasks;
 6
 7 namespace WindowsFormsApplication1
 8 {
 9     public class City
10     {
11         private int _id1;
12
13         public int Id1
14         {
15             get { return _id1; }
16             set { _id1 = value; }
17         }
18         private string _name;
19
20         public string Name
21         {
22             get { return _name; }
23             set { _name = value; }
24         }
25         private int _id2;
26
27         public int Id2
28         {
29             get { return _id2; }
30             set { _id2 = value; }
31         }
32     }
33 }

App.config:

1 <?xml version="1.0" encoding="utf-8" ?>
2 <configuration>
3     <startup>
4         <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.5" />
5     </startup>
6 <connectionStrings>
7   <add connectionString="Data Source =.; Initial Catalog = mysql; Integrated Security = True;" name="conStr" />
8 </connectionStrings>
9 </configuration>

数据库：