Local Notifications in Mobile App

Implementing Local Notifications in Mobile Apps

Local notifications — the only type that doesn't require a server at all. The app itself schedules them through the system API: at a specific time, by calendar trigger, or on geofence entry. Typical use cases — reminders, habit trackers, events in offline mode.

iOS: UNUserNotificationCenter

All APIs since iOS 10+ go through UNUserNotificationCenter. Three trigger types:

import UserNotifications

// 1. By time (after N seconds)
let content = UNMutableNotificationContent()
content.title = "Meeting reminder"
content.body = "Meeting with team in 15 minutes"
content.sound = .default
content.badge = 1

let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 900, repeats: false)
let request = UNNotificationRequest(identifier: "meeting-reminder-123",
                                    content: content,
                                    trigger: trigger)
UNUserNotificationCenter.current().add(request)

// 2. By date/time (repeating every day at 9:00)
var dateComponents = DateComponents()
dateComponents.hour = 9
dateComponents.minute = 0
let dailyTrigger = UNCalendarNotificationTrigger(dateMatching: dateComponents, repeats: true)

// 3. By geofence
let region = CLCircularRegion(center: CLLocationCoordinate2D(latitude: 50.45, longitude: 30.52),
                               radius: 200,
                               identifier: "office-zone")
region.notifyOnEntry = true
region.notifyOnExit = false
let geoTrigger = UNLocationNotificationTrigger(region: region, repeats: false)

Request identifier (identifier) — important. Use it to update or cancel notification:

// Update (overwrite existing)
UNUserNotificationCenter.current().add(updatedRequest) // same identifier

// Cancel
UNUserNotificationCenter.current().removePendingNotificationRequests(withIdentifiers: ["meeting-reminder-123"])

// View scheduled
UNUserNotificationCenter.current().getPendingNotificationRequests { requests in
    print("Pending: \(requests.count)")
}

iOS limit — 64 scheduled notifications per app. When exceeded, old ones are silently removed. For trackers with hundreds of reminders, you need a strategy: keep nearest N in queue, reschedule the rest when app opens.

Android: NotificationCompat + AlarmManager / WorkManager

Android has no unified "notification scheduler" — you need to save the time yourself, wake the app through AlarmManager and then show notification.

// Schedule through AlarmManager (exact time — requires SCHEDULE_EXACT_ALARM on Android 12+)
val alarmManager = context.getSystemService(AlarmManager::class.java)
val intent = Intent(context, NotificationReceiver::class.java).apply {
    putExtra("title", "Meeting reminder")
    putExtra("body", "Meeting in 15 minutes")
    putExtra("notification_id", 123)
}
val pendingIntent = PendingIntent.getBroadcast(context, 123, intent,
    PendingIntent.FLAG_UPDATE_CURRENT or PendingIntent.FLAG_IMMUTABLE)

alarmManager.setExactAndAllowWhileIdle(
    AlarmManager.RTC_WAKEUP,
    triggerAtMillis,
    pendingIntent
)

NotificationReceiver — a BroadcastReceiver that builds and shows notification:

class NotificationReceiver : BroadcastReceiver() {
    override fun onReceive(context: Context, intent: Intent) {
        val notification = NotificationCompat.Builder(context, "reminders_channel")
            .setSmallIcon(R.drawable.ic_notification)
            .setContentTitle(intent.getStringExtra("title"))
            .setContentText(intent.getStringExtra("body"))
            .setPriority(NotificationCompat.PRIORITY_HIGH)
            .setAutoCancel(true)
            .build()

        NotificationManagerCompat.from(context)
            .notify(intent.getIntExtra("notification_id", 0), notification)
    }
}

Important: AlarmManager resets on device reboot. You need to intercept BOOT_COMPLETED broadcast and reschedule all active reminders from local database (Room).

For Android 12+ exact alarms require SCHEDULE_EXACT_ALARM permission. For recurring reminders without exact time — better WorkManager with PeriodicWorkRequest, it survives reboot automatically.

Geofence Notifications

On iOS geofence notifications work through UNLocationNotificationTrigger (see above). On Android — through GeofencingClient:

val geofence = Geofence.Builder()
    .setRequestId("office-zone")
    .setCircularRegion(50.45, 30.52, 200f)
    .setExpirationDuration(Geofence.NEVER_EXPIRE)
    .setTransitionTypes(Geofence.GEOFENCE_TRANSITION_ENTER)
    .build()

val request = GeofencingRequest.Builder()
    .setInitialTrigger(GeofencingRequest.INITIAL_TRIGGER_ENTER)
    .addGeofence(geofence)
    .build()

geofencingClient.addGeofences(request, geofencePendingIntent)

Geofence notifications require ACCESS_FINE_LOCATION permission, and on Android 10+ — ACCESS_BACKGROUND_LOCATION. The latter is a separate request, user must explicitly select "Allow always" in settings.

Timeframe

Implementing local notifications by time and schedule, geofence triggers, correct reboot and limit handling — 3–6 working days depending on platforms.