When using Google push notifications, I am allowed to specify a collapse_key value so a device will not receive multiple notifications of the same collapse_key.
Does APNS have a similar feature or does anyone know a way to emulate this functionality?
As of iOS 10 and using the HTTP/2.0 APNS API, you can specify apns-collapse-id header and handle the collapse logic in your app.
Collapsed notifications will appear as one single notification on the device that keeps updating with new data. Each time a notification is updated it is pushed to the top of your unread notifications.
Description of apns-collapse-id taken from https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/CommunicatingwithAPNs.html:
Multiple notifications with same collapse identifier are displayed to
the user as a single notification. The value should not exceed 64
bytes. For more information, see Quality of Service,
Store-and-Forward, and Coalesced Notifications.
and from https://developer.apple.com/library/content/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/APNSOverview.html#//apple_ref/doc/uid/TP40008194-CH8-SW1:
When a device is online, all the notifications you send are delivered
and available to the user. However, you can avoid showing duplicate
notifications by employing a collapse identifier across multiple,
identical notifications. The APNs request header key for the collapse
identifier is apns-collapse-id and is defined in Table 6-2.
For example, a news service that sends the same headline twice in a
row could employ the same collapse identifier for both push
notification requests. APNs would then take care of coalescing these
requests into a single notification for delivery to a device.
With iOS 10 there is a new "apns-collapse-id" which looks like it will handle this sort of need. If you have an Apple developer account you can look at the WWDC 2016 notification session videos (707 intro video https://developer.apple.com/videos/play/wwdc2016/707/).
Doody P's answer works for remote notifications, but there is also an equivalent for locally triggered notifications: when you create your UNNotificationRequest, you can set the identifier parameter to whatever you had been using as a collapse key. After being triggered, the push notification will show only the latest version that you sent with that identifier.
(We send push notifications silently through APNs and then retrigger as local notifications, because we need to make sure that our users are logged in.)
There are handy code examples & demos of managing delivered notifications in this WWDC talk - the key section is from ~18:00 - 21:00.
If APNs attempts to deliver a notification but the device is offline,
the notification is stored for a limited period of time, and delivered
to the device when it becomes available.
Only one recent notification for a particular app is stored. If
multiple notifications are sent while the device is offline, each new
notification causes the prior notification to be discarded. This
behavior of keeping only the newest notification is referred to as
coalescing notifications.
https://developer.apple.com/library/ios/documentation/NetworkingInternet/Conceptual/RemoteNotificationsPG/Chapters/ApplePushService.html
So there's no need for collapse_key in iOS.
FYI, collapse_key is only useful when the device is offline/inactive:
This parameter identifies a group of messages (e.g., with
collapse_key: "Updates Available") that can be collapsed, so that only
the last message gets sent when delivery can be resumed. This is
intended to avoid sending too many of the same messages when the
device comes back online or becomes active (see delay_while_idle).
https://developers.google.com/cloud-messaging/server-ref#downstream
UPDATE:
For both iOS and Android (using collapse_key), if the device is offline (ie the Apple/Google push server cannot reach it), the push server overwrites any previous notification, and only keeps the last one.
If the device is online, then I guess it's up to you to do whatever you want with the received notification. At least in Android you can decide whether you want to "pile things up", whether you want to overwrite any previous notification in the notification area, or whether you want to overwrite any previous notification of the same type.
NotificationManager notificationManager = ...;
String appName = ...;
NotificationCompat.Builder builder = ...
// Always use the same id, so only the last notification will be displayed in the notification area.
int notId = 0;
// Always use a different id, so all notifications will pile up in the notification area
notId = new Random().nextInt(100000);
// Uses the type of notification as id, so you'll only have up to one notification per type
// in the notification area. It's like using collapse_key, but on the app itself.
// That type should should be some additional data in the notification you sent.
notId = notificationType;
Notification notification = builder.build();
notificationManager.notify(appName, notId, notification);
There is no such feature in iOS. However, since push notifications are sent by a server that is in your control, you can keep track of which notifications you've sent to a particular device, and decide whether or not to send new ones. In other words, you put the logic in your server code, not your iOS app code.
Related
Problem Statement : I'm using voip notification to show local notification.I'm trying to send notification from Apns to a offline device. So, It queued all pending notifications. But, It only send last queued notification once device becomes
online.
As per apple documentation Link
Quality of Service, Store-and-Forward, and Coalesced Notifications
Apple Push Notification service includes a Quality of Service (QoS)
component that performs a store-and-forward function. If APNs attempts
to deliver a notification and the destination device is offline, APNs
stores the notification for a limited period of time and delivers it
when the device becomes available again. This component stores only
the most recent notification per device and per app. If a device is
offline, sending a notification request targeting that device causes
the previous request to be discarded. If a device remains offline for
a long time, all its stored notifications in APNs are discarded.
To allow the coalescing of similar notifications, you can include a
collapse identifier within a notification request. Normally, when a
device is online, each notification request that you send to APNs
results in a notification delivered to the device. However, when the
apns-collapse-id key is present in your HTTP/2 request header, APNs
coalesces requests whose value for that key is the same. For example,
a news service that sends the same headline twice could use the same
collapse identifier value for both requests. APNs would then coalesce
the two requests into a single notification for delivery to the
device.
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:
Â
Â
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
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:
Â
Â
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
On Android, when supplying the same id in two calls to NotificationManager.notify, only one notification will be shown in the notification drawer.
But how to do it on iOS
Thanks
Notifications on iOS are not designed to be grouped/collapsed or replaced by other notifications. Just check other messenger apps, the convention is to have a separate notification for each message, contrary to Android. Also a message doesn't get replaced by a new message in the same conversation. The functionality that Android provides here simply doesn't exist in iOS.
What you could do instead is, to send silent notifications ("push-to-sync") and handle the grouping/replacing on client side, since you have more control over local notifications (e.g. you can remove single local notifications, but not single remote notifications). But keep in mind, if the app was force quit, it won't be woken up to process the silent notification.
I think your best option is to stick to the convention and don't group/replace notifications.
about iOS you have to understand many things about the push notification
first it is not part of your app, in iOS it is separate application called notification centre that your app add itself to it so when APNS send a notification it send it to the notification centre in your iPhone not to your app.
so what you need to do will be in the server side not in the mobile side
for example let's say it is a chat application
the server side should check if the message is sent from the same user
the badge count should remain the same and not to notify APNS with new count
and also in the server side
the server will check if the message from the same user to send only sound notification not text or if the server got many message at once from the same user send the text with got many message from same user
but all of that is just work around as something like this is not provided yet in iOS may be in iOS9 as it become more open and not like previous versions
good luck
I am using iOS push notifications. In Android you can set up to 4 notification keys and then using these keys you can have notifications replace prior notifications if they have not yet been read/seen by the user.
Do iOS push notifications also allow you to selectively replace prior notifications? (E.g. using a common notification key) or do they always "rack up" and cannot be replaced.
Link: Local and Push Notification Programming Guide:
Quality of Service
Apple Push Notification service includes a default Quality of Service
(QoS) component that performs a store-and-forward function.
If APNs attempts to deliver a notification but the device is offline,
the notification is stored for a limited period of time, and delivered
to the device when it becomes available.
Only one recent notification for a particular application is stored.
If multiple notifications are sent while the device is offline, each
new notification causes the prior notification to be discarded. This
behavior of keeping only the newest notification is referred to as
coalescing notifications.
If the device remains offline for a long time, any notifications that
were being stored for it are discarded.
There's no such mechanism in place in iOS.
After sending a push notification you have no control over it anymore.