1 namespace Province_City
 2 {
 3     public partial class Form1 : Form
 4     {
 5         public Form1()
 6         {
 7             InitializeComponent();
 8         }
 9 
10         private void Form1_Load(object sender, EventArgs e)
11         {
12            
13            string connStr= ConfigurationManager.ConnectionStrings["Connstr"].ConnectionString;
14 
15             using (SqlConnection conn = new SqlConnection(connStr))
16             {
17                 conn.Open();
18                 using (SqlCommand cmd = conn.CreateCommand())
19                 {
20                     cmd.CommandText = "select * from promary";
21                     using (SqlDataReader dataReader = cmd.ExecuteReader())
22                     {
23                         while (dataReader.Read())
24                         {
25                             ProvinceItem item = new ProvinceItem();
26                             item.Id = dataReader.GetInt32(dataReader.GetOrdinal("proId"));
27                             item.Name = dataReader.GetString(dataReader.GetOrdinal("proName"));
28                             comProvince.Items.Add(item);
29 
30                         }
31                     }
32                 }
33             }
34         }
35 
36 
37 
38         private void comProvince_SelectedIndexChanged(object sender, EventArgs e)
39         {
40 
41             ProvinceItem item = (ProvinceItem)comProvince.SelectedItem;
42             int proID = item.Id;
43 
44             
45            
46             string connStr = ConfigurationManager.ConnectionStrings["Connstr"].ConnectionString;
47         //using (SqlConnection conn = new SqlConnection(@"Data Source=HP-PC;Initial Catalog=DBPromary;User ID=sa;Password=123"))
48             using (SqlConnection conn = new SqlConnection(connStr))
49             {
50                 conn.Open();
51                 
52                 using (SqlCommand cmd = conn.CreateCommand())
53                 {
54                     cmd.CommandText = "select * from city where proID=@proID";
55                     cmd.Parameters.Add(new SqlParameter("proID", proID));
56                     using (SqlDataReader dataReader = cmd.ExecuteReader())
57                     {
58                         while (dataReader.Read())
59                         {
60                             string cityName = dataReader.GetString(dataReader.GetOrdinal("cityName"));
61                             comCity.Items.Add(cityName);
62                            
63                         }
64                     }
65                 }
66           }
67 
68         }
69 
70         class ProvinceItem
71         {
72             public string Name { get; set; }
73             public int Id { get; set; }
74         }
75 
76      
77     }
78 }