Unnotification with timedelay sometimes not working iOS swift

Solution:

I had faced the problem that i had give time for unnotification at a particular time like now or after few seconds.but sometimes it was not triggered.So i changed the code from

let trigger = UNCalendarNotificationTrigger(dateMatching: triggerDate,                                                repeats: true)

To

        let trigger = UNTimeIntervalNotificationTrigger(timeInterval: TimeInterval(delay),
                                                        repeats: false)

It was working good. If you want to trigger a notification to current time use the above code or if you want to trigger a notification at next hour or some date then use the dae based trigger.