iOS - aSyncAfter while app is in background - ios

Question

I'm attempting to run a a simple iOS application that pushes a notification to a user's screen after a specified time.
So far, this is what I have (borrowed from another thread):
DispatchQueue.global(qos: .background).async {
print( "background task" )
DispatchQueue.main.asyncAfter( deadline: .now() + milliseconds( 2000 )) {
let content = UNMutableNotificationContent()
content.body = "Testing :)"
content.badge = 1
let trigger = UNTimeIntervalNotificationTrigger( timeInterval: 2, repeats: false )
let request = UNNotificationRequest( identifier: "test", content: content, trigger: trigger )
UNUserNotificationCenter.current().add(request, withCompletionHandler: nil)
print( "background finish" )
}
}
My only issue is that the aSync After doesn't run whenever the app is in the background.
For example, if a user goes into their lockscreen or a different app, the notification never gets triggered.
Would anyone have a suggestion for how I could achieve this?
Thank you! :)

Answer 1

Approach:
Use UNNotificationRequest with time interval
Below mentioned solution would work in the following scenarios:
Foreground
Background
App is closed
Steps:
Set the delegate (to be alerted in foreground)
Request authorisation from user to be alerted
Create the notification
Add it to the notification center
AppDelegate:
AppDelegate must conform to UNUserNotificationCenterDelegate.
Set the notification center's delegate to the AppDelegate
import UserNotifications
#UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
// Override point for customization after application launch.
UNUserNotificationCenter.current().delegate = self
return true
}
//MARK: UNUserNotificationCenterDelegate
//This is required to be alerted when app is in foreground
func userNotificationCenter(_ center: UNUserNotificationCenter,
willPresent notification: UNNotification,
withCompletionHandler completionHandler: #escaping (UNNotificationPresentationOptions) -> Void) {
print("will present")
completionHandler([.alert, .badge, .sound])
}
func userNotificationCenter(_ center: UNUserNotificationCenter,
didReceive response: UNNotificationResponse,
withCompletionHandler completionHandler: #escaping () -> Void) {
print("did receive")
}
}
Setting up notification:
import UserNotifications
private func setupNotification() {
requestAuthorization { [weak self] isGranted, error in
if let error = error {
print("Request Authorization Error: \(error)")
return
}
guard isGranted else {
print("Authorization Denied")
return
}
self?.addNotification()
}
}
private func requestAuthorization(completionBlock: #escaping (Bool, Error?) -> ()) {
let center = UNUserNotificationCenter.current()
center.requestAuthorization(options: [.alert, .badge, .sound]) { isGranted, error in
completionBlock(isGranted, error)
}
}
private func addNotification() {
let content = UNMutableNotificationContent()
content.title = "Testing Notification"
content.body = "This is a test for notifications"
content.sound = .default()
let timeInterval = TimeInterval(5)
let trigger = UNTimeIntervalNotificationTrigger(timeInterval: timeInterval, repeats: false)
let request = UNNotificationRequest(identifier: "Something",
content: content,
trigger: trigger)
let center = UNUserNotificationCenter.current()
center.add(request) { error in
if let error = error {
print("Error adding notification request: \(error)")
}
else {
print("Successfully added notification request")
}
}
}