I have an application which has communication with a remote server. The server should push data into it using remote notification silently, and I need to get and store these data into a CoreData database. The user won't be aware of the whole process.
I can successfully get notified when the app receives a remote notification, while it is either in the foreground or background mode. However, I need to get data while the app is terminated as well.
I searched for the possible solutions. For example, this SO question was good if I don't tend to use silent notification. I also saw the PushKit capability, but I am not sure about the Apple Review result.
What is the possible solution?
If I want to use VoIP and PushKit to get notified when the app is terminated, would Apple reject my application?
If you’re not creating a VoIP app and you want your app to be in the App Store then the correct answer is: it is not possible. The only thing that can be done is adjusting your requirements in some way.
For instance you can send some notifications that will be visible for user in the Notification Center and wait until the user taps the notification or starts the app the usual way. Then the app will be able to do all the operations you need.
The delivery of push notifications is not guaranteed, so you should not rely on them to synchronise data.
For example, if multiple push notifications are sent while the device is offline, only the last notification is delivered when the device comes back online; the earlier notifications are lost.
When your app launches one of the first things it should do is check with your server for new data.
Related
While working with APNS, I was able to have push notifications work flawlessly while device is online.
For any APNS push I send while device is offline, only the last one is received once the device is back online. This seems to be coherent with Apple's Store-and-Forward design.
However - I did notice, that when sending WhatsApp messages to an offline device, once this device goes online it receives all push notifications (one for each message). This is not something based on collapse identifier, but rather independent push notification for each message.
So how did WhatsApp do it?
Tried using Notification Extension and attempt to post multiple local notifications, but this also fails as extensions are not allowed to do that.
Instead of a normal push notification, use a Background Notification, which will not show anything visible, but wake up your app in background. Use this event, to make api call, get relevant data and generate multiple local notifications.
Note the following from the documentation when you implement application(_:didReceiveRemoteNotification:fetchCompletionHandler:) :
system calls this method when your app is running in the foreground or background
system does not automatically launch your app if the user has force-quit it
you must call the block in the handler parameter (fetchCompletionHandler) or your app will be terminated. Your app
has up to 30 seconds of wall-clock time to process the notification
and call the specified completion handler block
Apps that use significant amounts of power when processing remote notifications may not always be woken up early to process future
notifications
Please read relevant documentation completely before making ANY assumptions about how you think this should work.
Since push notifications may not be delivered sometimes (you can lose a few of them), you can not run code after the iPhone is turned on to check if there is new information available from the server, and you can not run code if your iOS App is closed... What can you do if you want to be as more accurate as possible in for example a Chat App in iOS?
I mean, inform the user as faster as possible that he has new info available. Comparisons: WhatsApp is updated without any delay.
You can do background fetch if your App is in background. But if the App is closed and you miss a push, it's not going to be up to date until the next push arrives or user opens the App. The same with silent notifications. If the app is terminated by the user, you are not going to receive it. Is there any way to solve it? It must be because other Apps do it... If there is any "private and secret" API that they are using (I read about this answer when no one know how to do that)... Is there any way to apply to use it?
UPDATE:
I'm using push notifications. The goal is to fix when a push doesn't arrive. Example: User A send chat message to user B. User B doesn't have the App open. The system lose the push. User B is not going to receive the message until he open the App.
Push notifications seems to be your only way even if you do loose a few of them, which I don't know how you would since they are pushed to apples secure server... but what do I know. As long as the user turns on the push notifications you should be fine. They may be delayed due to apples way of handling them. Honestly push seems to be the future, having your app constantly every minute or two check for new messages is a huge battery water in conjunction with normal texting apps. Your app should provide the best live data but since apple restricts to push notifications when the app is off or not running just stick to push notifications and only push major events to the user. I believe you can set up a job scheduler using quartz or schedulator to setup your server to push notifications to your app.
I have implemented AWS SNS push notification service.
We have an issue which is explained below :
Scenario :
We are trying to save the notification message we receive as a part of requirement.
When the app is killed (swipe out from recent apps) we are able to receive notification, also we are able to save the notification message when we open the message directly from the notification panel it works fine,but when we open the app directly the notification message is not getting saved.
In short we are not able to know if we had received a notification message if we directly open the app rather than clicking the message from the notification panel.
Is this default behavior ? or is there any work around for this ?
Have looked into many posts on about Push Notifications but haven't seen any threads pointing to this scenario.
This is a normal behavior, and there is no workaround.
If your app is killed by the user, it won't be able to run ANY code before it's manually launched again.
If it's manually launched from a notification, this notification's payload will be handled by your AppDelegate.
On top of that, don't forget that Push notifications are Best Effort. That means that they are not reliable, they can be heavily delayed or never delivered at all. Don't rely on Push notifications to achieve any critical work.
If you need to keep a copy of your notifications in-app, keep them server side and fetch them as you would do with any other object.
In order to execute code when the app is killed by the user you need to implement VOIP using PushKit framework provided by apple.
VOIP push unlike regular push notification enables the app to become active even if the app is killed by user.
a simple question: is it possible to get a message, notification or similar when the internet connection is available when app is killed or not running?
For my purpose, I need a way to synchronize all my notifications because APNs can send only the last message.
EDIT:
I'm wondering how some apps (e.g. whatsapp) are able to sync their notifications when the internet connection is up. If I kill whatsapp, I can receive multiple notification when internet connection is reachable, but the APNS server provides only last message and, for this case, I'm not able to send silent notification. If I should develop a chat application, what are the best practices to work with Apple notifications?
If you send a push notification with a title, text, sound and/or badge property while the app is suspended (was killed / force closed), the device will still receive it, e.g. will show the text as a notification, play a sound and/or change the badge count.
However, your app won't be launched or woken up in the background in this case, so you have no way to handle the notification before the user taps on it. (See this question:
Will iOS launch my app into the background if it was force-quit by the user?)
So if the app was force closed by the user, your only option is to send a notification to be displayed as it is and if the device is offline, only the last notification will be received and displayed by the device.
For more control, you could use silent push notifications to implement "push-to-sync". In this case, the push notification only signals that there is new data to be fetched. The app (if not force closed) loads the data from the server then and triggers local notifications with the right data in the right order. But this won't work, if the app was force closed.
Apple push notifications have a lot of restrictions, so you won't be able to implement a perfect solution. In my opinion, it's fine if the user gets only the last notification when the device gets online after being offline for a while. At least he is informed that there is a new message and after opening the app, he can see the other new messages too. For the "push-to-sync" scenario, I would say that the user has no right to expect that the app works as desired, if he force-quits it.
Push notifications were never intended to be used in the way they are used by a lot of apps by now. E.g. they shouldn't contain sensitive data such as a chat message. They were intended to inform the user that there is new data for the app, so he can launch it to see the new data. E.g. instead of sending the actual chat message text a push notification should just contain the text "You have a new message". Then, you don't have the problem you described. Of course this is a terrible solution in terms of usability.
It is widely known that:
app doesn't receive push notification if it is in background or offline mode (app gets it once after user's action: tap on notification or app icon).
Apple push Notification service keep only ONE last notification when device is offline. Once device is connected to internet, APNs sends the last notification.
How to solve this?
very latest notification that just reached the app (not device) must reflect the actual number of notifications that are not implemented in the app yet. So, then I can download from the server last n notifications and implement them in the app at any time.
The question is:
How the server knows what notifications were implemented in the app, and which one not?
Notifications must be per device. Why? For instance, notification "remove object from Core Data" must be implemented in every device. Because only one user can be logged in on multiply devices at time.
You should track the state of the task (delete record or whatever your app needs to do) on the server and have the client report back when the task is done. Then flag the task as done.
Don't use push notifications as a reliable delivery method for your tasks, you will fail. Use the notifications as complementary part of your setup.
So for example when your app receives a notification, it can sync with the backend, to retrieve the tasks flagged as not done, execute them and then let the backend know that it's done.