号码归属地~~~~~跟视频里的一样却报错了~~~ - 黑马程序员技术交流社区

public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void Form1_Load(object sender, EventArgs e)
{
using (SqlConnection conn = new SqlConnection(@"Data source=.\SQLEXPRESS;AttachDBFilename=|DataDirectory|\DB.mdf;
integrated Security=True;User Instance=True"))
{
conn.Open();
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "select * from Province";
using (SqlDataReader dataReader = cmd.ExecuteReader())
{
while (dataReader.Read())
{
Province item = new Province();
item.Name = dataReader.GetString(dataReader.GetOrdinal("proName"));
item.Id = dataReader.GetInt32(dataReader.GetOrdinal("proId"));
cmbProvince.Items.Add(item.Name);
}
}
}
}
}
private void cmbProvince_SelectedIndexChanged(object sender, EventArgs e)
{
Province item = (Province)cmbProvince.SelectedItem; //此句报错
int proid = item.Id;
using (SqlConnection conn = new SqlConnection(@"Data source=.\SQLEXPRESS;AttachDBFilename=|DataDirectory|\DB.mdf;
integrated Security=True;User Instance=True"))
{
conn.Open();
using (SqlCommand cmd = conn.CreateCommand())
{
cmd.CommandText = "select * from City where proId=proid";
cmd.Parameters.Add(new SqlParameter("proId", proid));
using (SqlDataReader dataReader = cmd.ExecuteReader())
{
while (dataReader.Read())
{
string ctName = dataReader.GetString(dataReader.GetOrdinal("cityName"));
cmbCity.Items.Add(ctName);
}
}
}
}
}
}
class Province
{
public string Name { get; set; }
public int Id { get; set; }
}

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