如何将选定的数据库列添加到C＃组合框中？

Question

这是我用C＃编写的简单代码，当我更改索引时，subject_name被添加到没有数据库值的组合框中。

private void gradebox_SelectedIndexChanged(object sender, EventArgs e) 
{ 
    SqlConnection con = new SqlConnection(conString); 
    con.Open(); 

    if (con.State == System.Data.ConnectionState.Open) 
    { 
     String num = gradebox.SelectedItem.ToString(); 
     string q = "SELECT subject_name FROM subjects WHERE grade = '"+num+"'"; 
     Console.Write(gradebox.Text.ToString()); 
     // SqlDataReader dr = q.ExecuteReader(); 
     SqlCommand cmd = new SqlCommand(q, con); 

     SqlDataReader dr = cmd.ExecuteReader(); 

     while (dr.Read()) 
     { 
      subbox.Items.Add("subject_name"); 
     } 
    } 
} 

Answer 1

你需要得到从SqlDataReader的数据看Read data from SqlDataReader

while (dr.Read()) 
{ 
    subbox.Items.Add(dr.GetString(0)); 
}