MySqlDataReader 为啥一到while (reader.Read())就catch退出

MySqlDataReader 为什么一到while (reader.Read())就catch退出?
在webService里的:

C# code

using (MySqlConnection conn = CreateConnection()) {     MySqlCommand cmd = new MySqlCommand(sql, conn);     MySqlDataReader reader = cmd.ExecuteReader();                    while (reader.Read())     {        Depart d1 = new Depart();        d1.Qsectionnaem = reader["qsectionname"].ToString();        depart.Add(d1);     }}

一到这里就catch退出,报错是说conn must avalid andopen，我用using(conn){}应该不是这个问题吗？求解答

C# code

     while (reader.Read())     {        Depart d1 = new Depart();        d1.Qsectionnaem = reader["qsectionname"].ToString();        depart.Add(d1);     }

------解决方案--------------------
using (MySqlConnection conn = CreateConnection())
 {
conn.Open();
MySqlCommand cmd = new MySqlCommand(sql, conn);
MySqlDataReader reader = cmd.ExecuteReader();

while (reader.Read())
{
Depart d1 = new Depart();
d1.Qsectionnaem = reader["qsectionname"].ToString();
depart.Add(d1);
}
}