weak var deviceUnlockedObserver: NSObjectProtocol?
weak var deviceLockedObserver: NSObjectProtocol?
var isDeviceLocked = true

private func addDeviceUnlockedObserver() {
        guard deviceUnlockedObserver == nil else {return}

        deviceUnlockedObserver = NotificationCenter.default.addObserver(forName: .UIApplicationProtectedDataDidBecomeAvailable, object: nil, queue: .main) { (noti) in
            DispatchQueue.main.async {
                self.isDeviceLocked = false
            }
        }
    }

private func addDeviceLockedObserver() {
    guard deviceLockedObserver == nil else {return}

    deviceLockedObserver = NotificationCenter.default.addObserver(forName: .UIApplicationProtectedDataWillBecomeUnavailable, object: nil, queue: .main) { (noti) in
        DispatchQueue.main.async {
            self.isDeviceLocked = true
        }
    }
}

private func removeObserver() {
    if let unlockObserver = deviceUnlockedObserver {
        NotificationCenter.default.removeObserver(unlockObserver)
    }
    if let lockedObserver = deviceLockedObserver {
        NotificationCenter.default.removeObserver(lockedObserver)
    }
}