How to send local notification UNTimeInterval starting at specific time in swift [iOS]

Question

I want to send a local notification every 8 hours starting at specific time. For example, now we are at 10 o'clock in the morning, but I want you to notify me every 8h starting at 12 o'clock, how I can do that.

I have this code:

let content: UNMutableNotificationContent = UNMutableNotificationContent()
content.title = "Alert!"
content.body = "Alert"
content.categoryIdentifier = "alarm"

let request = UNNotificationRequest(
    identifier: "AA",
    content: content,
    trigger: UNTimeIntervalNotificationTrigger(timeInterval: 8*3600, repeats: false)
)

let action = UNNotificationAction(identifier: "remindLater", title: "remind_me_later".localized(), options: [])
let category = UNNotificationCategory(identifier:"pill-alarm", actions: [action], intentIdentifiers: [], options: [])

UNUserNotificationCenter.current().setNotificationCategories([category])
UNUserNotificationCenter.current().add(request)

Answer 1

So i had the same problem what i end up doing was:

Let's say you have an alarm every 8 hours, starting at 12 and now is 10AM well i did some calculations and created several repeating notifications:

first Notification will be everyday at 12, second Notification will be everyday at 20, third Notification will be everyday at 4.

you create them like this:

var date = DateComponents()
date.hour = hour
date.minute = minutes

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

let request = UNNotificationRequest(identifier: notificationId, content: content, trigger: trigger)

center.add(request) { (error) in
    if let error = error {
        print("Error \(error.localizedDescription)")
    }
}

You need to set diferent identifiers to them, so you can do first,second,third or numerate them. this will help you if you need to cancel them at some point.

Answer 2

First you need to create a trigger date instead of time interval

Like this :

let date = Date(timeIntervalSinceNow:  8*3600 + extraTime) // extraTime = time interval between 8 to 12
let triggerDate = Calendar.current.dateComponents([.year,.month,.day,.hour,.minute,.second,], from: date)

Now use trigger date in request

let request = UNNotificationRequest(
    identifier: "AA",
    content: content,
    trigger: UNTimeIntervalNotificationTrigger(timeInterval: triggerDate, repeats: false)
)

for more reference : https://useyourloaf.com/blog/local-notifications-with-ios-10/