[ios] Detect if the app was launched/opened from a push notification

I'll start with a state chart that I created for my own use to visualize it more accurately and to consider all other states: https://docs.google.com/spreadsheets/d/e/2PACX-1vSdKOgo_F1TZwGJBAED4C_7cml0bEATqeL3P9UKpBwASlT6ZkU3iLdZnOZoevkMzOeng7gs31IFhD-L/pubhtml?gid=0&single=true

Using this chart, we can see what is actually required in order to develop a robust notification handling system that works in almost all possible use cases.

Complete solution ?

  • Store notification payload in didReceiveRemoteNotification
  • Clear stored notification in applicationWillEnterForeground and didFinishLaunchingWithOptions
  • To tackle cases where control Center/ Notification center pulled, you can use a flag willResignActiveCalled and set it to false initially, Set this to true in applicationWillResignActive method,
  • In didReceiveRemoteNotification method, save notifications(userInfo) only when willResignActiveCalled is false.
  • Reset willResignActiveCalled to false in applicationDidEnterBackground and applicationDidBecomeActive method.

Note: A Similar answer is suggested in comments on Eric's answer, however, the state sheet helps in finding all possible scenarios as I did in my app.

Please find the complete code below and comment below if any specific case is not handled:

AppDelegate

class AppDelegate: UIResponder, UIApplicationDelegate {
  private var willResignActiveCalled = false

  func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    NotificationUtils.shared.notification = nil
    return true
  }
  func applicationWillResignActive(_ application: UIApplication) {
    willResignActiveCalled = true
  }
  func applicationDidEnterBackground(_ application: UIApplication) {
    willResignActiveCalled = false
  }
  func applicationWillEnterForeground(_ application: UIApplication) {
    NotificationUtils.shared.notification = nil
  }
  func applicationDidBecomeActive(_ application: UIApplication) {
    willResignActiveCalled = false
    NotificationUtils.shared.performActionOnNotification()
  }
  func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
    if !willResignActiveCalled { // Check if app is in inactive by app switcher, control center, or notification center
      NotificationUtils.shared.handleNotification(userInfo: userInfo)
    }
  }
}

NotificationUtils : This is where you can write all your code to navigating to different parts of the application, handling Databases(CoreData/Realm) and do all other stuff that needs to be done when a notification is received.

   class NotificationUtils {
  static let shared = NotificationUtils()
  private init() {}

  var notification : [AnyHashable: Any]?

  func handleNotification(userInfo : [AnyHashable: Any]){
    if UIApplication.shared.applicationState == UIApplicationState.active {
      self.notification = userInfo //Save Payload
      //Show inApp Alert/Banner/Action etc
      // perform immediate action on notification
    }
    else if UIApplication.shared.applicationState == UIApplicationState.inactive{
      self.notification = userInfo
    }
    else if UIApplication.shared.applicationState == UIApplicationState.background{
      //Process notification in background,
      // Update badges, save some data received from notification payload in Databases (CoreData/Realm)
    }
  }

  func performActionOnNotification(){
    // Do all the stuffs like navigating to ViewControllers, updating Badges etc
    defer {
      notification = nil
    }
  }
}

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