当没有找到结果时,处理ExecuteScalar返回null

Question

我有这个代码可能返回没有找到结果 - null

 String result
 string searchUby = "SELECT text FROM rooms WHERE year=@year AND event=@eventAND text=@text AND z is NULL";
                SqlCommand sqlcom = new SqlCommand(searchUby, conn);
                sqlcom.Parameters.AddWithValue("@event",event.Text);
                sqlcom.Parameters.AddWithValue("@text", cb_room.SelectedItem);
                sqlcom.Parameters.AddWithValue("@year",klientClass.Year());
                conn.Open();                  
                result = sqlcom.ExecuteScalar().ToString(); // on this line ex occurs

                conn.Close();

我得到这个例外:

NullReferenceException: Object reference not set to an instance of an object. 

愿有人帮我解决这个问题吗？

Answer 1

试试这个:

result = (sqlcom.ExecuteScalar() ?? "").ToString();

如果返回null,则结果为空字符串.您可以通过if语句处理该情况并向用户通知一些消息,例如:

object r = sqlcom.ExecuteScalar();  
if(r != null) result = r.ToString();
else {
  //code to handle the null case here...
}