已有打开的与此命令相关联的 DataReader，必须首先将它关闭。
求大神解决一下。已经用reader.Close()了。怎么还错误！
public static tbBook GetBookById(string BId)
        {
            string sql = "select * from tb_Book where Bookid =@Bookid";
            using (SqlDataReader reader = connDBHelper.GetReader(sql, new SqlParameter("@Bookid", BId)))
            {
                
                try
                {


                    if (reader.Read())
                    {
                        tbBook book = new tbBook();
                        book.Bookid = (string)reader["Bookid"];
                        book.Bookname = (string)reader["Bookname"];
                        book.Bookclass = BookClassService.GetBookClassById((int)reader["Bookclass"]);
                        book.Author = (string)reader["author"];
                        book.Image = (string)reader["image"];
                        book.Publish = (string)reader["publish"];
                        book.Banci = (string)reader["banci"];
                        book.Price = (double)reader["price"];
                        book.Language = (string)reader["language"];
                        book.Page = (int)reader["page"];
                        book.Number = (int)reader["number"];
                        book.Kuc = (int)reader["kuc"];
                &nb