Home iOS & Swift Books Push Notifications by Tutorials

8
Handling Common Scenarios Written by Scott Grosch

As you noticed in previous projects in this book, iOS will automatically handle presenting your notifications as long as your app is in the background or terminated. But what happens when it is actively running? In that case, you need to decide what it is that you want to happen. By default, iOS simply eats the notification and never displays it. That’s pretty much always what you want to happen, right? No? Didn’t think so!

In the download materials for this chapter, you’ll find possibly the coolest starter project that’s ever been created.

sarcasm
ˈsär-ˌka-zəm
noun
the use of irony to mock or convey contempt

Displaying foreground notifications

If you’d like to have iOS display your notification while your app is running in the foreground, you’ll need to implement the UNUserNotificationCenterDelegate method userNotificationCenter(_:willPresent:withCompletionHandler:), which is called when a notification is delivered to your app while it’s in the foreground. The only requirement of this method is calling the completion handler before it returns. Here, you can identify what you want to happen when the notification comes in.

Note: After opening up the starter project for this chapter, remember to turn on the Push Notifications capability as discussed in Chapter 4, “Xcode Project Setup,” and set the team signing as discussed in Chapter 7, “Expanding the Application.”

Conform to the aforementioned protocol in your AppDelegate. At the bottom of AppDelegate.swift, write the following:

extension AppDelegate: UNUserNotificationCenterDelegate {
  func userNotificationCenter(
    _ center: UNUserNotificationCenter, 
    willPresent notification: UNNotification, 
    withCompletionHandler completionHandler: 
    @escaping (UNNotificationPresentationOptions) -> Void) {
    
    completionHandler([.alert, .sound, .badge])
  }
}

Probably one of the most complex methods you’ve ever written, right?

You’re simply telling the app that you want the normal alert to be displayed, the sound played and the badge updated. If the notification doesn’t have one of these components, or the user has disabled any of them, that part is simply ignored.

If you want no action to happen, you can simply pass an empty array to the completion closure. Depending on the logic that pertains to your app, you may want to investigate the notification.request property of type UNNotificationRequest and make the decision about which components to show based on the notification that was sent to you.

In order for the delegate to be called, you have to tell the notification center that the AppDelegate is the actual delegate to use.

Make a couple changes to your registerForPushNotifications(application:) back in ApnsUploads.swift:

func registerForPushNotifications(application: UIApplication) {
  let center = UNUserNotificationCenter.current()
  center.requestAuthorization(options: [.badge, .sound, .alert]) {
    // 1
    [weak self] granted, _ in

    // 2
    guard granted else {
      return
    }

    // 3
    center.delegate = self

    DispatchQueue.main.async {
      application.registerForRemoteNotifications()
    }
  }
}

There are three simple changes made:

  1. Capture a weak reference to self in the completion handler.
  2. Then, make sure you have been granted the proper authorization to register for notifications.
  3. Finally, you just need to set the UNUserNotificationCenter’s delegate to be the AppDelegate object.

Build and run your app. Now, use the tester app (as described in Chapter 5, “Apple Push Notifications Servers”) to send a push notification while you’re in the foreground. You should see it displayed this time! You can use the following simple payload for testing purposes:

{
  "aps": {
    "alert": {
      "title": "Hello Foreground!",
      "body": "This notification appeared in the foreground."
    }
  }
}

You should get a notification on your device with your app still in the foreground!

Tapping the notification

The vast majority of the time when a push notification arrives, your end users won’t do anything except glance at it. Good notifications don’t require interaction, and your user gets what they need at a glance. However, that’s not always the case. Sometimes your users actually tap on the notification, which will trigger your app to be launched.

func userNotificationCenter(
  _ center: UNUserNotificationCenter, 
  didReceive response: UNNotificationResponse, 
  withCompletionHandler completionHandler: @escaping () -> Void) {
  
  defer { completionHandler() }

  guard response.actionIdentifier == 
      UNNotificationDefaultActionIdentifier else {
    return
  }
  
  // Perform actions here
}

Handle user interaction

By default, tapping on the notification simply opens up your app to whatever the “current” screen was — or the default startup screen, if the app was launched from a terminated state.

import UIKit
import UserNotifications

final class NotificationDelegate: NSObject, 
  UNUserNotificationCenterDelegate {
  
  func userNotificationCenter(
    _ center: UNUserNotificationCenter, 
    willPresent notification: UNNotification, 
    withCompletionHandler completionHandler: 
    @escaping (UNNotificationPresentationOptions) -> Void) {
    completionHandler([.alert, .sound, .badge])
  }

  func userNotificationCenter(
    _ center: UNUserNotificationCenter, 
    didReceive response: UNNotificationResponse, 
    withCompletionHandler completionHandler: @escaping () -> Void) {
    defer { completionHandler() }

    guard 
      response.actionIdentifier == UNNotificationDefaultActionIdentifier 
    else {
      return
    }

    // Perform actions here
  }
}
center.delegate = self?.notificationDelegate
let payload = response.notification.request.content
guard payload.userInfo["beach"] != nil else { return }

let storyboard = UIStoryboard(name: "Main", bundle: nil)
let vc = storyboard.instantiateViewController(withIdentifier: "beach")

let appDelegate = UIApplication.shared.delegate as! AppDelegate
appDelegate.window!.rootViewController!.present(vc, animated: false)
{
  "beach": true,
  "aps": {
    "alert": {
      "body": "Tap me!"
    }
  }
}

Silent notifications

Sometimes, when you send a notification, you don’t want the user to actually get a visual cue when it comes in. No alert or sound, for example.

Updating the payload

The first step to take is simply adding a new key-value pair to your payload. Inside of the aps dictionary, add a new key of content-available with a value of 1. This will tell iOS to wake your app when it receives a push notification, so it can prefetch any content related to the notification.

{
  "aps": {
    "content-available": 1
  },
  "image": "https://bit.ly/2Iodl06",
  "text": "A nice picture of the Earth"
}

Adding background modes capability

Next, back in Xcode, you’ll need to add a new capability just as you did at project creation.

App delegate updates

When a silent notification comes in, you’ll want to make sure that it contains the data you’re expecting, updates your Core Data model, and then tells iOS you’re done processing.

func application(
  _ application: UIApplication, 
  didReceiveRemoteNotification userInfo: [AnyHashable : Any], 
  fetchCompletionHandler completionHandler: 
  @escaping (UIBackgroundFetchResult) -> Void) {
  
  guard let text = userInfo["text"] as? String,
        let image = userInfo["image"] as? String,
        let url = URL(string: image) else {
    completionHandler(.noData)
    return
  }
}
// 1
let context = persistentContainer.viewContext
context.perform {
  do {
    // 2
    let message = Message(context: context)
    message.image = try Data(contentsOf: url)
    message.received = Date()
    message.text = text

    try context.save()
  
    // 3
    completionHandler(.newData)
  } catch {
    // 4
    completionHandler(.failed)
  }
}

Method routing

The following table shows you which methods are called, and in what order, depending on whether your app is in the foreground or background, and whether or not the content-available flag (i.e., silent notification) is present with a value of 1.

Key points

  • For iOS to display your notification while your app is running in the foreground, you’ll need to implement a UNUserNotificationCenterDelegate method, which is called when a notification is delivered to your app while it’s in the foreground.
  • Good notifications don’t require interaction, and your user gets what they need at a glance. Some notifications are tapped, however, which triggers an app launch. You will need to add an additional method in your AppDelegate.swift file.
  • Sometimes, you want a tapped notification to open a specific view controller within your app. You will need to add an additional method to handle this routing.
  • Silent notifications give no visual or audible cue. To enable silent notifications, you’ll need to update the payload, add the Background Modes capability, and implement a new UIApplicationDelegate method.

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