数据为空。无法在Null值C＃上调用此方法或属性

Question

我使用的是SQL Server数据库，我有一些错误代码：

  offerDayCount = (int)reader["day"];

我收到以下错误：

  

数据为空。无法在Null值上调用此方法或属性

我尝试了以下操作：

offerDayCount = reader.GetInt32(reader.GetOrdinal("day") as int? ?? 0);

和：

if (reader[“day”] != null)
              offerDayCount = (int)reader["day"];

还有更多代码行：

using (SqlCommand com = new SqlCommand("select ID,month,day,startdate,endDate,offer from [enddate] where ID=@ID", con))
                {
                    com.Parameters.AddWithValue("@ID", ID.Text);
                    using (SqlDataReader reader = com.ExecuteReader())
                    {
                        if (reader.Read())
                        {
                            //get information from enddate table
                            var offer = reader["offer"].ToString();
                            offerDayCount = (int)reader["day"];
                            startDate = (DateTime)reader["startDate"];
                            if (reader["endDate"] != null)
                                endDate = (DateTime)reader["endDate"];


                            if (reader["month"] == null && offer != null)
                            {
                                endDate = DateTime.Now.Date;
                            }
                        con.Close();
                        con.Open();
                            //count the visit from checkin table
                            using (var com2 = new SqlCommand("SELECT COUNT(*) as count From checkin WHERE time >= @STARTDATE and (time <= @ENDDATE)",con))
                            {
                                com2.Parameters.AddWithValue("@STARTDATE", startDate);
                                com2.Parameters.AddWithValue("@ENDDATE", endDate);

                                using (SqlDataReader reader2 = com2.ExecuteReader())
                                {
                                    if (reader2.Read())
                                    {
                                        visitedCount = (int)reader2["count"];
                                        if (offer != null && visitedCount < offerDayCount)
                                            goodForVisit = true;

                                        if (offer != null && DateTime.Now >= startDate && DateTime.Now <= endDate)
                                            goodForVisit = true;
                                    }
                                }
                            }
                        }
                    }
                }

您能帮我解决我的问题吗？