title: swift 4 notification not appearing when app is in background
body: <p>My code below is firing the notification the way it should when the app is in use. However when I exit out of the app the notification does not appear. I have listed both my view controller and app delegate code. I thought I put the correct code in App Delegate. I am not sure why this is not working. </p>
  
  <p>VIEW CONTROLLER</p>
  
  <pre><code>   import UIKit
  import AVFoundation
  import UserNotifications
  
  let center = UNUserNotificationCenter.current() // usernotification center
  
  class ViewController: UIViewController, UNUserNotificationCenterDelegate {
      var timer = Timer()
      var isGrantedAccess = false
      var player: AVAudioPlayer?
      var passingDate : Date?
      @IBOutlet var dptext: UITextField!
      let datePicker = UIDatePicker()
      @IBOutlet var taskIDo: UITextView!
  
      override func viewWillAppear(_ animated: Bool) {
  
          center.delegate = self
          createDatePicker()
          timer  = Timer.scheduledTimer(timeInterval: 10, target: self, selector: #selector(testDate), userInfo: nil, repeats: true)
  
      }
  
      func playSound() {
          let url = Bundle.main.url(forResource: "fc", withExtension: "mp3")!
          do {
              player = try AVAudioPlayer(contentsOf: url)
              guard let player = player else { return }
  
              player.prepareToPlay();player.play()} catch let error as NSError {print(error.description)}}
  
  
      func createDatePicker() {
          datePicker.datePickerMode = .dateAndTime
          let toolbar = UIToolbar()
          toolbar.sizeToFit()
  
          let doneButton = UIBarButtonItem(barButtonSystemItem: .done, target: nil, action: #selector(donePressed))
          toolbar.setItems([doneButton], animated: false)
  
          dptext.inputAccessoryView = toolbar;dptext.inputView = datePicker
      }
  
      @objc func testDate() {
          print("in testDate")
          if Calendar.current.isDate(datePicker.date, equalTo: Date(), toGranularity: .minute) {
              if let passingDate = passingDate, Calendar.current.isDate(datePicker.date, equalTo: passingDate, toGranularity: .minute)
              {
                  print("in return")
                  return
              }
  
              passingDate = datePicker.date
  
              setNotification()
  
          }
      }
      func setNotification() {
          let content = UNMutableNotificationContent()
          content.title = "This is Title"
          content.subtitle = "This is subTitle"
  
          content.sound = UNNotificationSound.default()
  
          let trigger = UNTimeIntervalNotificationTrigger(timeInterval: 10.0, repeats: false)
  
          let request = UNNotificationRequest(identifier: "Identifier", content: content, trigger: trigger)
  
          UNUserNotificationCenter.current().add(request) { (error) in
  
              print(error?.localizedDescription ?? "")
          }
  
      }
      @objc func donePressed() {
  
          let dateFormatter = DateFormatter()
          dateFormatter.dateStyle = .short
          dateFormatter.timeStyle = .short
          dptext.text = dateFormatter.string(from: datePicker.date)
          self.view.endEditing(true)
  
      }
  }
  </code></pre>
  
  <p>APPDELEGATE</p>
  
  <pre><code>import UIKit
  import UserNotifications
  
  @UIApplicationMain
  class AppDelegate: UIResponder, UIApplicationDelegate, UNUserNotificationCenterDelegate {
  
      var window: UIWindow?
  
  
  
      func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -&gt; Bool {
          // Override point for customization after application launch.
  
          UNUserNotificationCenter.current().requestAuthorization(options:
              [.badge,.alert,.sound])
          {
              (sucess,error) in
              if error != nil {
                  print("Error Found, \(error?.localizedDescription ?? "")")
  
              } else {
                  print("Authorized by the user")
              }
          }
  
          UNUserNotificationCenter.current().delegate = self
          return true
      }
  
      func applicationWillResignActive(_ application: UIApplication) {
          // Sent when the application is about to move from active to inactive state. This can occur for certain types of temporary interruptions (such as an incoming phone call or SMS message) or when the user quits the application and it begins the transition to the background state.
          // Use this method to pause ongoing tasks, disable timers, and invalidate graphics rendering callbacks. Games should use this method to pause the game.
      }
  
      func applicationDidEnterBackground(_ application: UIApplication) {
          // Use this method to release shared resources, save user data, invalidate timers, and store enough application state information to restore your application to its current state in case it is terminated later.
          // If your application supports background execution, this method is called instead of applicationWillTerminate: when the user quits.
      }
  
      func applicationWillEnterForeground(_ application: UIApplication) {
          // Called as part of the transition from the background to the active state; here you can undo many of the changes made on entering the background.
      }
  
      func applicationDidBecomeActive(_ application: UIApplication) {
          // Restart any tasks that were paused (or not yet started) while the application was inactive. If the application was previously in the background, optionally refresh the user interface.
      }
  
      func applicationWillTerminate(_ application: UIApplication) {
          // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
      }
  
  
  }
  </code></pre>