Xcode 10 Swift 4.2
To show Push Notification when your app is in the foreground - 
Step 1 : add delegate UNUserNotificationCenterDelegate in AppDelegate class.
class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {
Step 2 : Set the UNUserNotificationCenter delegate
let notificationCenter = UNUserNotificationCenter.current()
notificationCenter.delegate = self
Step 3 : This step will allow your app to show Push Notification even when your app is in foreground
func userNotificationCenter(_ center: UNUserNotificationCenter,
                                willPresent notification: UNNotification,
                                withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        completionHandler([.alert, .sound])
    }
Step 4 : This step is optional. Check if your app is in the foreground and if it is in foreground then show Local PushNotification.
func application(_ application: UIApplication,didReceiveRemoteNotification userInfo: [AnyHashable: Any],fetchCompletionHandler completionHandler:@escaping (UIBackgroundFetchResult) -> Void) {
        let state : UIApplicationState = application.applicationState
        if (state == .inactive || state == .background) {
            // go to screen relevant to Notification content
            print("background")
        } else {
            // App is in UIApplicationStateActive (running in foreground)
            print("foreground")
            showLocalNotification()
        }
    }
Local Notification function - 
fileprivate func showLocalNotification() {
        //creating the notification content
        let content = UNMutableNotificationContent()
        //adding title, subtitle, body and badge
        content.title = "App Update"
        //content.subtitle = "local notification"
        content.body = "New version of app update is available."
        //content.badge = 1
        content.sound = UNNotificationSound.default()
        //getting the notification trigger
        //it will be called after 5 seconds
        let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 1, repeats: false)
        //getting the notification request
        let request = UNNotificationRequest(identifier: "SimplifiedIOSNotification", content: content, trigger: trigger)
        //adding the notification to notification center
        notificationCenter.add(request, withCompletionHandler: nil)
    }