Local notification sound not playing while app in background - Swift

I'm making an alarm clock app, and I have confirmed that my alarm notifications are being triggered correctly, but the sound does not always play as I expect.

For instance, when the phone is not in silent mode, the notification plays the sound sucessfully (ok, great!). However, when the phone is in silent mode, the sound does not play, even though the app is still running in the background (not so great...).

I understand that silent mode is supposed to silence all notification sounds, BUT I've downloaded other alarm clock apps from the App Store (like Alarmy), and they are somehow able to get their notification sounds to play even if the phone is on silent mode, as long as the app is still running in the background. Only when the app is fully exited will the silent mode take effect.

Does anyone know how to achieve this result? Is there some setting or option that I need to declare either in my code or plist file? I've scoured the internet but haven't found anything for this particular issue...

My code to set the AVAudioSession category:

private func setAudioCategory() {
    do {
        // Enable sound (even while in silent mode) as long as app is in foreground.
        try AVAudioSession.sharedInstance().setCategory(.playback)
    }
    catch {
        print(error.localizedDescription)
    }
}

My code to set a notification:

/// Sets a local user notification for the provided `Alarm` object.
static func set(_ alarm: Alarm) {

    // Configure the notification's content.
    let content = UNMutableNotificationContent()
    content.title = NSString.localizedUserNotificationString(forKey: K.Keys.notificationTitle, arguments: nil)
    content.body = NSString.localizedUserNotificationString(forKey: K.Keys.notificationBody, arguments: nil)

    // Get sound name
    let soundName: String = UserDefaultsManager.getAlarmSound().fileNameFull
        
    // Set sound
    content.sound = UNNotificationSound(named: UNNotificationSoundName(rawValue: soundName))
    content.categoryIdentifier = "Alarm"

    // Configure the time the notification should occur.
    var date = DateComponents()
    date.hour = alarm.hour
    date.minute = alarm.minute

    // Create the trigger & request
    let trigger = UNCalendarNotificationTrigger(dateMatching: date, repeats: false)
    let request = UNNotificationRequest(identifier: alarm.notifID, content: content, trigger: trigger)

    // Schedule the request with the system.
    let notificationCenter = UNUserNotificationCenter.current()
    notificationCenter.add(request, withCompletionHandler: { error in
        if error != nil {
            // TODO: Show Alert for Error
            return
        }
    })
}

So I've discovered something.

As the question is stated, it is not currently possible to play sound in a local notification when the phone is on silent mode.

However, great news!

There is actually a different way to achieve the same result; and it's how apps like Alarmy do it.

Note: I (FINALLY) discovered this solution from this wonderful SO answer, but I'll summarize it here for reference.

In short, the local notification will not be playing the sound, but instead, the app will play it (while in the background).

STEPS

1. You must enable the app to play sound in the background. To do this, navigate to your .plist file and add the String value App plays audio or streams audio/video using AirPlay to the array key Required background modes. (This can also be achieved in your app's Capabilities - it does the same thing).

2. In your App Delegate, set your AVAudioSession's category to .playBack so sound will still play even when the phone is locked or in the background.

do {
    try AVAudioSession.sharedInstance().setCategory(.playAndRecord)
    try AVAudioSession.sharedInstance().setActive(true)
} catch {
    print(error.localizedDescription)
}

3. Start your AVAudioPlayer at the time you would like it to play (in my case, at the time of my local notification).

let timeInterval = 60.0 // 60.0 would represent 1 minute from now
let timeOffset = audioPlayer.deviceCurrentTime + timeInverval
audioPlayer.play(atTime: timeOffset) // This is the magic function

// Note: the `timeInterval` must be added to the audio player's 
// `.deviceCurrentTime` to calculate a correct `timeOffset` value.

In conclusion, as the SO answer I linked to above so aptly summarizes:

This does not play silence in the background, which violates Apple's rules. It actually starts the player, but the audio will only start at the right time. I think this is probably how Alarmy implemented their alarm, given that it's not a remote notification that triggers the audio nor is the audio played by a local notification (as its not limited to 30 seconds or silenced by the ringer switch).