Why userNotificationCenter didReceive is not fired?

问题

This is a part of my code. I want to use UNUserNotificationCenter and UNUserNotificationCenterDelegate to handle notification events.

This code catches the notification event when the app is in a foreground state. But "didReceive" is not fired for a background state.

func application(_ application: UIApplication,
                         didFinishLaunchingWithOptions launchOptions:
            [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
            UNUserNotificationCenter.current().delegate = self
    application.registerForRemoteNotifications()
    return true
    }    
        func userNotificationCenter(_ center: UNUserNotificationCenter,
                                    willPresent notification: UNNotification,
                                    withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void)
        {
            print("willPresent") /// This works
            completionHandler([.alert, .badge, .sound])
        }
        func userNotificationCenter(_ center: UNUserNotificationCenter,
                                    didReceive response: UNNotificationResponse,
                                    withCompletionHandler completionHandler: @escaping () -> Void) {
            print("didReceive") /// This doesn't work
            completionHandler()
        }

But if I don't use UNUserNotificationCenter.current().delegate = self the delegate method is correctly fired in the background.

func application(_ application: UIApplication,
                     didReceiveRemoteNotification userInfo: [AnyHashable: Any],
                     fetchCompletionHandler completionHandler: @escaping FetchCompletionHandler) {
        print("didReceiveRemoteNotification... \(userInfo)")
}

How can I use "didReceive"? I want to handle the notification in the background.

回答1:

application(_:didReceiveRemoteNotification:fetchCompletionHandler:) is called when the application receives a silent push notification. Silent push notifications can be delivered in when the application is in the background state, iOS wakes the application to perform background processing invisible to the user.

A silent push notification has the content-available flag set to 1.

Silent push notifications should not include an alert, badge, or sound. Silent push is not meant to be visible to the user, it is only a hint to the application that new remote content is available.

Removing the content-available flag from your push notification payload will cause iOS to handle it as a regular notification. The user notification center delegate methods will be called instead of application(_:didReceiveRemoteNotification:fetchCompletionHandler:) but your application will be unable to do background processing triggered by the notification.

You can validate the content of your push notification payload for problems like this using this tool

回答2:

This is how I handle push notification in my app. I think you need to implement all of these methods to handle all iOS versions in the foreground and background mode.

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {

    if #available(iOS 10.0, *) {
        let center  = UNUserNotificationCenter.current()
        center.delegate = self
        center.requestAuthorization(options: [.sound,.alert,.badge], completionHandler: { (granted, error) in
            if error == nil {
                DispatchQueue.main.async {
                    application.registerForRemoteNotifications()
                }
            }
        })
    }
    else {
        let notificationTypes: UIUserNotificationType = [UIUserNotificationType.alert, UIUserNotificationType.badge, UIUserNotificationType.sound]
        let pushNotificationSettings = UIUserNotificationSettings(types: notificationTypes, categories: nil)
        application.registerUserNotificationSettings(pushNotificationSettings)
        application.registerForRemoteNotifications()
    }

}

func application(_ application: UIApplication, didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data) {
    let deviceTokenString = deviceToken.reduce("", {$0 + String(format: "%02X", $1)})
    print(deviceTokenString)
}

func application(_ application: UIApplication, didFailToRegisterForRemoteNotificationsWithError error: Error) {
    print("Failed to get token; error: \(error)")
}

@available(iOS 10.0, *)
func userNotificationCenter(_ center: UNUserNotificationCenter, willPresent notification: UNNotification, withCompletionHandler completionHandler: @escaping (UNNotificationPresentationOptions) -> Void) {
    completionHandler([.alert,.sound])
     //do sth
}

@available(iOS 10.0, *)
func userNotificationCenter(_ center: UNUserNotificationCenter, didReceive response: UNNotificationResponse, withCompletionHandler completionHandler: @escaping () -> Void) {
     //do sth
}

// for iOS < 10
func application(_ application: UIApplication, didReceive notification: UILocalNotification) {
}

func application(_ application: UIApplication, didReceiveRemoteNotification userInfo: [AnyHashable : Any], fetchCompletionHandler completionHandler: @escaping (UIBackgroundFetchResult) -> Void) {
}

回答3:

There are methods of UNUserNotificationCenterDelegate:

willPresent: This method gets called when you receive a notification when your app is in the foreground. If the app is in the background then this method will not calls.
didRecieve: This method gets called when a user clicked on the notification.

In case of background state, only 'didRecieve' will be called when user will click on a notification.

来源：https://stackoverflow.com/questions/53460280/why-usernotificationcenter-didreceive-is-not-fired

标签

ios

swift

push-notification

unusernotificationcenter