SwiftUI Remote Push Notifications without AppDelegate - Is it Possible?

Question

I have implemented push notifications in my SwiftUI app and everything seems to work fine. As you know there is no AppDelegate but we can still use @UIApplicationDelegateAdaptor.

However I don't like this approach and I'm wondering if there is a way to implement this without having an AppDelegate?

class AppDelegate: NSObject, UIApplicationDelegate {
    private var gcmMessageIDKey = "gcmMessageIDKey"
    
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
        Messaging.messaging().delegate = self
        
        // For iOS 10 display notification (sent via APNS)
        UNUserNotificationCenter.current().delegate = self
        
        let authOptions: UNAuthorizationOptions = [.alert, .badge, .sound]
        UNUserNotificationCenter.current().requestAuthorization(options: authOptions, completionHandler: {_, _ in })
        
        application.registerForRemoteNotifications()
        
        return true
    }
    
    func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any]) {
        // If you are receiving a notification message while your app is in the background,
        // this callback will not be fired till the user taps on the notification launching the application.
        // TODO: Handle data of notification
        
        // With swizzling disabled you must let Messaging know about the message, for Analytics
        // Messaging.messaging().appDidReceiveMessage(userInfo)
        
        // Print message ID.
        if let messageID = userInfo[gcmMessageIDKey] {
            print("Message ID: \(messageID)")
        }
        
        // Print full message.
        print(userInfo)
    }
    
    func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable: Any],
                     fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
        // If you are receiving a notification message while your app is in the background,
        // this callback will not be fired till the user taps on the notification launching the application.
        // TODO: Handle data of notification
        
        // With swizzling disabled you must let Messaging know about the message, for Analytics
        // Messaging.messaging().appDidReceiveMessage(userInfo)
        
        // Print message ID.
        if let messageID = userInfo[gcmMessageIDKey] {
            print("Message ID: \(messageID)")
        }
        
        // Print full message.
        print(userInfo)
        
        completionHandler(UIBackgroundFetchResult.newData)
    }
    
}

extension AppDelegate : UNUserNotificationCenterDelegate {
    
    // Receive displayed notifications for iOS 10 devices.
    func userNotificationCenter(_ center: UNUserNotificationCenter,
                                willPresent notification: UNNotification,
                                withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
        let userInfo = notification.request.content.userInfo
        
        // With swizzling disabled you must let Messaging know about the message, for Analytics
        // Messaging.messaging().appDidReceiveMessage(userInfo)
        
        // Print message ID.
        if let messageID = userInfo[gcmMessageIDKey] {
            print("Message ID: \(messageID)")
        }
        
        // Print full message.
        print(userInfo)
        
        // Change this to your preferred presentation option
        completionHandler([[.banner, .sound]])
    }
    
    func userNotificationCenter(_ center: UNUserNotificationCenter,
                                didReceive response: UNNotificationResponse,
                                withCompletionHandler completionHandler: @escaping () -> Void) {
        let userInfo = response.notification.request.content.userInfo
        // Print message ID.
        if let messageID = userInfo[gcmMessageIDKey] {
            print("Message ID: \(messageID)")
        }
        
        // With swizzling disabled you must let Messaging know about the message, for Analytics
        // Messaging.messaging().appDidReceiveMessage(userInfo)
        
        // Print full message.
        print(userInfo)
        
        completionHandler()
    }
}

extension AppDelegate: MessagingDelegate {
    func messaging(_ messaging: Messaging, didReceiveRegistrationToken fcmToken: String?) {
        print("Firebase registration token: \(String(describing: fcmToken))")
        
        let dataDict:[String: String] = ["token": fcmToken ?? ""]
        NotificationCenter.default.post(name: Notification.Name("FCMToken"), object: nil, userInfo: dataDict)
        // TODO: If necessary send token to application server.
        // Note: This callback is fired at each app startup and whenever a new token is generated.
        
        // Add a new document in collection "cities"
        
        guard let registrationToken = fcmToken else { return }
        guard let uid = Auth.auth().currentUser?.uid else { return }
        
        let db = Firestore.firestore()
        
        db.collection("users").document(uid).updateData(["registrationToken": registrationToken]) { err in
            if let err = err {
                print("Error writing document: \(err)")
            }
        }
    }
}

Answer 1

Does this link answer your question? Quoting:

You can use @UIApplicationDelegateAdaptor to provide an AppDelegate:

class AppDelegate: NSObject, UIApplicationDelegate {

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
        return true
    }
}
@main struct SampleApp: App {
    @UIApplicationDelegateAdaptor private var appDelegate: AppDelegate
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

I'm just in the research phase on how to do this though so your probably ahead of me. But it looks like as the name might imply the @UIApplicationDelegateAdaptor allows you to use an AppDelegate generated in the code above.

This other link maybe explains it better. It seems to be a lot like using UIKit inside SwiftUI.