When I read Apple Docs, they mention 3 types of notification: local, remote, and silent.
Local notification can be inferred from its name, that is sent by the app locally.
However, what is the difference between the other two types?
EDIT: While this answer is fully applicable, there are some additions (not changes) to notifications in iOS 12. I highly recommend watching WWDC 2018: What’s New in User Notifications and read this amazing and must read article.
Main changes are:
grouped notifications along with summary format
provisional notifications ie show notifications directly in notification center without user permission
critical notifications which ignore 'do not disturb' or 'mute'
ability to interact with the notifications in the extensions
ability to completely reset or update actions
ability to deeplink into app's notification Settings from phone's Notification Center
IMPORTANT NOTE: Not sure since when but from the Apple docs, the 'silent notification' has been renamed to 'background notification'
There are too many settings that need to be set right for it to work. I'll try to dissect them and make them easier to understand.
Overall, several things are important.
the overall difference between a silent and user notification
different types of user notifications
how a remote notification, i.e. the payload, is configured from your server
how to enable push notifications and remote notifications from background modes on your project
how to register your token with APNs for remote and silent notifications and APNs architecture
how to request permission for user notifications
enabling 'background app refresh' and 'notifications' from the device
what is content-available
understanding that the iOS is upstream to your app when it comes to receiving a remote notification
what happens when the OS receives notifications when the app has been user-terminated
A note on reliability and APNs architecture
I highly recommend everyone to watch the first 7 minutes of: WWDC 2015: What's new in Notifications. From there, the presenter mentions that there are 2 major types of notifications:
Silent Notifications
They happen in the background, hence you never see any alert/badge/sound. Things get downloaded without you knowing about them.
iOS 11 bug
See here.
iOS 11 initial releases were buggy for silent notifications. Make sure
you have the latest version for your testing, otherwise, it may not
work
User Notifications
As the name says, it has something to do with the user. That is, the user will see an alert/badge or hear a sound. It has 2 types.
Local Notifications
A Local Notification can be triggered in 3 different ways:
UNLocationNotificationTrigger:
You see an alert when you're close to a Walmart store.
UNTimeIntervalNotificationTrigger: e.g. You see an alert every 10 minutes.
UNCalendarNotificationTrigger like December 1st 1:00PM 2017.
Remote Notifications
They are similar to local notifications but they are triggered from the server, e.g. a WhatsApp message that has a From field (Mom) and a body field (I love you!).
Token registration and APNs architecture:
To receive a silent or remote notification, you need to register for a token using:
application.registerForRemoteNotifications()
👆 Registering does NOT require user permission. This makes silent notifications to become seamless. See this moment of the WWDC video
Silent notifications are enabled by default. The user does not need
to approve your -- does not give permission to your app to use them,
and you can just start using them without asking the user for
permission.
From WWDC
Remember APNs is delivered to your users by APNs and not by your server. So your iOS code must send this token to your server. So the server can associate a given device token with the user. When you want to push to a certain user, your server just tells APNs to send a payload to a specific token. What's important to understand is that your server and APNs are two different things
The flow of it looks like this:
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server/provider sends a payload to APNs
APNs send a notification to all target devices of a given account. e.g. your iPhone, Mac could both receive notifications for emails/messages.
Then your iPhone/Mac will deliver that message to the app. APNs don't directly send messages to your app. It sends it to the device. Then the iOS sends it to your app.
For more on this see docs APNs Overview and Sending Notification Requests to APNs
To be able to show badges/alerts/sounds, you need to request permission from the user:
UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .badge, .sound]) { (granted, error) in
guard error == nil else {
//Display Error.. Handle Error.. etc..
return
}
if granted {
//Do stuff here..
//Register for RemoteNotifications. Your Remote Notifications can display alerts now :)
application.registerForRemoteNotifications()
}
else {
//Handle user denying permissions..
}
}
Question: Do I need to request access once for local notifications and once for remote notifications?
No. Just write the snippet above and it will request access for both remote and local.
Now let's get to the tricky part :D
Xcode Project + iPhone Settings
Do I need to enable something to receive silent notifications?
You must enable Push Notifications from your Xcode capabilities:
If you don't enable this, your app won't receive a token. And without a token, the server doesn't recognize you.
To be able to download stuff from the background, you need to enable: remote notifications from background modes.
To enable backgroundModes, you can do it either using your plist or Xcode capabilities.
The reason you can do it, either way, is because plist is closer to your code and is the old way, perhaps it's there for legacy support. Xcode capabilities is the newer, easy way.
plist:
Item 0 is just an index, it's not the key of a dictionary (something you normally see in plist), the UIBackgroundModes is an array of Strings. The strings must only come from an accepted value from the UIBackgroundModes Array.
Xcode Capabilities:
Check the Remote Notification in Xcode under background modes as below:
If you don't do any of the above, then toggling off notifications with:
will kill Remote & Local Notifications
However, if you do enable background app refresh from plist or Xcode capabilities, then even with notifications turned off for the app, you will still receive silent notifications!
If the user wants to disable silent notifications, he would have to disable both notifications and disable 'background app refresh for your app / across the system.
To disable 'background app refresh' across your system, you have to do this:
Why am I saying all this? To explain to you that settings of silent and push notifications are different for the user and the restrictions for sending them are different. For more, see this moment from the WWDC video. See here instead (the previous link was dead):
Silent notifications are enabled by default.
The user does not need to approve your does not give permission to
your app to use them, and you can just start using them without asking
the user for permission.
But silent notifications are the mechanism behind background app
refresh.
At any point you know that the user can go in settings and disable
them.
So you can't depend on them always being available.
You don't know if the user the turn them off, and you are not getting
a notification anymore.
This also means that silent notifications are delivered with the best
effort.
That means that when the notification arrives on the user's device,
the system is going to make some choices.
It's going to use different signals from the device and from the user
behavior, like power or the time of day to decide when it is a good
time to deliver the notification and launch your app.
It may try to save battery or it may try to match the user behavior
and make the content available when the user is more likely to use it.
Also see here.
CAVEAT: Even if you disable app background refresh and disable allow notifications, you can still receive silent notifications if your app is in FOREGROUND. If your app is in the background, it won't be delivered.
Do I need to enable something to receive remote notifications?
You just need to enable Push Notifications from your Xcode capabilities:
If you don't enable this, your app won't receive a token. And without a token, the server doesn't recognize you.
APNs Payload structure
Curious... Can you tell me what should my payload look like?
I highly recommend you see Apple§ documentation. It's very clear AND ALSO SEE Sending Notification Requests to APNs. Basically platform makes an HTTP/2 call to APNs and sends the desired payload. Sending the correct headers is critical otherwise your notifications are not delivered to the devices!
Thanks, but can you just tell me the important parts?
uhhmm... OK, but just so you know this is from the link I just said:
For Silent Notifications there is a single criterion:
The payload's aps dictionary must include the content-available key
with a value of 1.
Per docs you can send other fields
If there are user-visible updates that go along with the background
update, you can set the alert, sound, or badge keys in the aps
dictionary, as appropriate.
A sample payload would look like this:
{
"aps" : {
"content-available" : 1
},
"acme1" : "bar",
"acme2" : 42
}
acme1, acme2, or just some custom data! But for the aps key, you MUST follow Apple's structure, otherwise, it won't map correctly and you won't be able to read data correctly.
Note: I haven't verified this, but another engineer mentioned that if you have provisional notifications enabled then to ensure silent notifications are delivered you must include an alert field with an empty body. For example:
{
"aps" : {
"content-available" : 1,
"alert" : {
"body" : "",
},
},
}
For User Notifications:
You need an alert key inside your aps.
As an example:
{
"aps" : {
"alert" : "You got your emails.",
"badge" : 9,
"sound" : "bingbong.aiff"
},
"acme1" : "bar",
"acme2" : 42
}
There is also a third option which I will discuss further down the answer.
As for what the fixed aps and alert dictionary keys are, see these Apple docs.
OK, got it. What is content-available?
Very simple. It's just a flag that tells your app that you need to wake up and download something because I have content available for download! For more info, see this exact moment.
By default the content-available flag is not included, i.e., by default the notifications you send won't trigger application(_:didReceiveRemoteNotification:fetchCompletionHandler:) or do something in your app. It would just show the notification. If you want to wake up the app (to do something in the background), you need to include content-available and set it to 1.
§: If you're using Firebase, your payload structure and keys may be slightly different. For example, the key content-available is replaced by content_available. For more, see Firebase documentation and also here.
I know you told me that I can only download something into my app when I'm using silent notifications, but is there a way that I can also wake my app up in the background AND download something for remote notifications?
Yes, but then similar to the silent notification, you must also set the content-available flag to 1, so it would know to wake up and download something. Otherwise, it would just pop and alert/badge/sound but won't download anything.
IMPORTANT NOTES:
If your app has only silent notifications, just enable "push notifications" + "remote notifications" from capabilities and set content-available to 1 for each payload.
If your app has only remote notifications, just enable "push notifications" from capabilities. There's nothing to do for the content-available.
However, if you want your notifications to show an alert/badge/sound and also download something in the background, you must have both "remote notifications" and "push notifications" enabled + set content-available to 1.
(THIRD OPTION)
{
"aps" : {
"content-available" : 1
"alert" : "You got your emails.",
"badge" : 9,
"sound" : "bingbong.aiff"
},
"acme1" : "bar",
"acme2" : 42
}
This moment from WWDC video mentions the 👆
To Quote the Apple Engineer:
Now, you can in a user remote notification, you can set the same
content available flag that you set in silent notifications, and that
allows your app to have some time to download the content or update
the content that it wants to be displayed so that when the user taps
on the notification, your content is available. And the user sees what
it does. This is a way to have a silent notification inside a user
notifications like a summary.
Notifications and iOS Application life-cycle
I'm confused about remote notifications. I thought whenever I get a notification, my app becomes active in the background and downloads something. Can you explain?
e.g. at this moment:
Your iPhone has just received a remote notification with a body of "no sender". To receive this, WhatsApp ** doesn't** have to be running in the background, i.e., you don't need "Remote Notifications" enabled from BackgroundModes. You would still receive the notification even if your app was force-quit or suspended because the process is managed by the OS, not the WhatsApp app. However, if you want to be able to download the actual message or its image/video to WhatsApp (so that once your user opens WhatsApp, the video would be sitting there waiting for the user), well then you need your app to become active. To do so, you need content-available : 1 and implement application(_:didReceiveRemoteNotification:fetchCompletionHandler:) .
Similarly, if you disable cellular data for an app, you would still receive its notifications. However, by tapping on that notification, the user won't be able to make any network requests for that app. They would only be able to open the app.
Or as for another similar scenario, if the server/access point you're connected to has restricted access for, say, WhatsApp, it would still allow you to receive the APNs notifications. However, by tapping on that notification, the user won't be able to make any network requests for that app. They would only be able to open the app.
CAVEAT: If the app was force-quit by the user, then while you do get the notification for the above-mentioned reasons, you can't do anything to bring the app out of its terminated state automatically (even if you had content-available set to 1). None of your delegate methods would be hit. The user must open the app and only then your delegate methods will be reached.
A note on reliability and APNs architecture:
Although notifications are heavily used to deliver the actual content to the app, they are somewhat NOT designed to deliver content to the app. Rather, they are designed to notify the user that "hey something new has arrived (a 2b message or a 50kb small image, or a 10MB image or a 2 GB video). Open the app if you like. By the way, here's a small piece of it (the actual message itself if it can fit, the title of the image or a thumbnail shown in the notification, a title of the video or a thumbnail shown in the video". For more, see iOS APNs “best-effort” fallback. To repeat, you never download the 40MB attachment sent in the email. You just get notified of its existence. You send just enough (a thumbnail view of the attachment) so that the user is informed of what's new and can decide whether or not they need to open the app for more. When I was new to iOS, I thought you actually send the image/video through the push notification. You don't!
Specifically in the case of silent notifications:
When a device receives a background notification, the system may hold
and delay the delivery of the notification, which can have the
following side effects:
When the system receives a new background notification, it discards the older notification and only holds the newest one.
If something force quits or kills the app, the system discards the held notification.
If the user launches the app, the system immediately delivers the held notification.
Pushing Background Updates to Your App docs
APNs sends a limited number of silent notifications—notifications with the content-available key—per day. In addition, if the device has already exceeded its power budget for the day, silent notifications are not sent again until the power budget resets, which happens once a day. These limits are disabled when testing your app from Xcode. See Pushing Background Updates to Your App.
Troubleshooting tips for handling errors returned from ANPs
Even for remote user notifications, the user may be off of the internet and this could cause expired content or APNs could throttle you if you're sending notifications too many or too quickly. See here again
Long story short the APNs and OS are King and you're beneath it. Hence you cannot rely on it to conform to your every command. Having that said it's super reliable in the sense that you see most messaging apps utilize it successfully.
Addendum How to generate push notification certificate, .p12 or .pem and how to test it all out?
Just see this terrific answer. It has the most number of screenshots I've ever seen.
The push notification will let the user know that they receive a notification (Showing the notification popup for example). The silent notification will update, but the user won't get notified about it.
In any case, you can perform actions when notified with silent, just as if it was a push notification. The only difference is the user will not get notify with the popup notification.
With push notification:
With silent notification:
The difference is in the payload:
Push notification:
aps {
content-available: 1
alert: {...}
}
Silent notification:
aps {
content-available: 0
alert: {...}
}
And you have to set in Capabilities the background mode you choose.
Silent push notification reaches device, user does not know anything about the notification but his app gets the notification and app will be given some time to download new content and present it to the user, regardless to the state of the app (i.e. running or not running)
Remote push notification method is called only when your app is running. If app is suspended or not running, then the system wakes up or launches your app and puts it into the background running state before calling the method.
This method is intended for showing the updated content to the user.When this method is called, your app has up to 30 seconds of wall-clock time to perform the download operation and call the specified completion handler block. If the handler is not called in time, your app will be suspended.
For more technical details, you can go through this links:
Apple Notifications
Silent Notifications
Is there any way to handle remote notification payloads before they’re delivered and display in notification centre?
With push notifications of default type there is no way to filter out notifications if the app is not in foreground.
The possible solution to this is to use VoIP push notifications in conjunction with PushKit.
VoIP pushes are always waking up the application, however they are not presented to the user and don't modify app badge value, so it's up to the developer to show a local notification upon the received VoIP push and to deal with app badge.
There is a technique with additional silent push that for example Facebook is using, to delete notification on iOS device when the message has been read on desktop web site. It's described here: https://www.pushwoosh.com/docs/deletable-ios-push
I build xcode app that get push notification, the main problem is that the push notification is very critical for me.
so I want to check if the push notification is delivered to the device with the app installed, I understand that if the iphone dosn't have internet connecction / 3G the push notification is not getting to the device.
how can I check if the device get the notification or not?
how can I check if the APNS successful to deliver the push notification?
I want to send sms if the push notification is not deliver to the device so I think about the idea to get the notification event when it's open by the push notification, and to send request to my server so i can know if the push notification is successful deliver or not. the main problem is that the user need to open the app every time he get the notification and in the night it's a problem. so this option is not good for me.
I check the feedback server push notification but i don't find any info that I can get if the push notification is delivered or not
any idea??
With iOS7 you have a new method called
application:didReceiveRemoteNotification:fetchCompletionHandler:
which you probably could use for your task. From Apple's Docs:
Implement this method if your app supports the remote-notification background mode.
...
When a push notification arrives, the system displays the notification to the user and
launches the app in the background (if needed) so that it can call this method. Use this
method to download any data related to the push notification. When your method is done,
call the block in the handler parameter.
Unlike the application:didReceiveRemoteNotification: method, which is called only when
your app is running, the system calls this method regardless of the state of your app.
The short answer, you can't, since APNS is one way. However, since an app can execute arbitrary code upon receipt of a notification, you can use this to say, send an http request to your own server when the notification is recieved.
There are any number of reason why push notifications might not get delivered to your user, or might not be delivered in a timely manner. Apple does not provide any mechanism for you to query the status of a push notification that you have sent.
If your app is currently running on the user's device and the user is accepting notifications for your app, you can implement the following method in your app delegate. It would be called whenever a push notification is received and in this method you could send a request back to your server to indicate the message was received. However this will only work while the user is running your app.
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo
In general though, it sounds like you'e relying on push notifications for something you shouldn't. From Apple's Local and Push Notification Programming Guide:
Important Because delivery is not guaranteed, you should not depend on
the remote-notifications facility for delivering critical data to an
application via the payload. And never include sensitive data in the
payload. You should use it only to notify the user that new data is
available.
There is no way to find out whether the notification was delivered to the device or no. APNS is a one way service. If there is no internet connection on the device then the APNS server will hold the last notification for some period of time which is no specified by Apple. If a new notification is sent to APNS for delivery then the old notification data is lost and replaced by the new data if its undelivered. If the notification is delivered then also the old notification data is deleted on the APNS server.
Please go through the following link : Apple Push Notification
Hope this helps you...........
If you are using JAVAPNS to send the APNS notification, you can use the below:
List<PushedNotification> notifications =
Push.combined("alert", badge, "default", "cert.p12", "certpassword", true, deviceToken);
for (PushedNotification notification : notifications) {
if (notification.isSuccessful()) {
//Push is successful. Do your thing...
}
else {
//Push is not successful. Do your thing...
}
}
I have a VoIP app, where the incoming call notification is very important.
The problem is, sometimes I don't get the push notification (even Apple said it's not guaranteed). But, I do have a mechanism to notice that an call is coming while the app is in the background.
So, what I want to do is.. still use Push Notification as the main handler for incoming call (because it handles the situation when app is closed). However, if the push notification failed to deliver and my app gets the call invite, I will raise a local notification, telling user that you have an incoming call.
My question is... how can I check if a notification is showing before I decide whether to fire a local notification?
AFAIK you can only detect the notification when the user taps on the banner OR if the app is open when the notification comes. So I can't see a way to detect if the notification has come yet or not. Just adding to the pain, push notification is famous for its unreliability.
There’s no API to get any information about the state of your notifications. Since you’re making a VoIP app, you have the option to have it get woken up for incoming data, which would let you post your “incoming call” notification whenever you need it—see the “Configuring Sockets for VoIP Usage” section here.