You can modify the content or presentation of arriving notifications using app extensions. To modify the content of a remote notification before it is delivered, use a notification service app extension. To change how the notification’s content is presented onscreen, use a notification content app extension.

Modifying the Payload of a Remote Notification

Use a notification service app extension to modify the payload of a remote notification before it is delivered to the user. Remote notifications originate from a server, which has control over the configuration and contents of the notification. A service extension lets your app make changes to the server-provided payload data before that data is presented to the user. You use service extensions to implement the following types of behaviors:

• Decrypt data that was delivered in an encrypted format.

• Download images or other media files and add them as attachments to the notification.

• Change the body or title text of the notification.

• Add a thread identifier to the notification or modify the contents of the notification’s userInfo dictionary.

The default notification service extension target provided by Xcode contains a subclass of the UNNotificationServiceExtension class for you to modify. Use the didReceiveNotificationRequest:withContentHandler: method to create and configure a new UNMutableNotificationContent object. You can make any changes you want to the new content object, replacing some or all of the original content values. When you are done, call the provided completion handler with your new content object. The system integrates your new content into the notification and delivers it to the user.

The system gives you a limited amount of time to modify the notification and call the provided completion handler, so you should perform any tasks quickly. If your didReceiveNotificationRequest:withContentHandler: method takes too long to call the completion handler, the system calls the serviceExtensionTimeWillExpire method to give you one final opportunity to finish your modifications. If you do not call the completion handler in time, the system displays the notification’s original content.

Remote notifications sent by your server must be crafted explicitly to support modification by a notification service app extension. Notifications that do not include the proper modifications are delivered directly to the user without modification. When creating the payload for the remote notification, your server should do the following:

• Include the mutable-content key with a value of 1.

• Include an alert dictionary with subkeys for the title and body of the alert.

For more information about implementing the methods of your notification service app extension, see UNNotificationServiceExtension Class Reference. For information about configuring the payload for remote notifications, see Creating the Remote Notification Payload.

Presenting Notifications Using a Custom Interface on iOS

Use a notification content app extension to display a custom user interface for your app’s notifications. You use an extension of this type to incorporate custom content or to use a different layout than the default interface. For example, you might use this type of extension to display images or media files inline with your notifications.

A notification content app extension supports the presentation of local and remote notifications associated with a specific category. You specify the category for a local notification using the categoryIdentifier of your UNNotificationContent object. For remote notifications, your server includes a category key with an appropriate value in the aps dictionary of the payload. When a notification with that category arrives, the system loads the view controller from your extension and incorporates your content into the system interfaces. You use the notification contents to configure your view controller before it appears onscreen.

The initial notification content app extension target is configured to present notifications associated with a single category. You must modify your target to specify which category of notifications you want to support with each extension. You specify the category using the UNNotificationExtensionCategory key in your target’s Info.plist file. Set the value of the key to the same string in the identifier property of the UNNotificationCategory object that your app registers at launch time.

You may include multiple notification content app extensions in your iOS app bundle. The system expects only one extension to support a given category, so you must configure the UNNotificationExtensionCategory key of each extension with a different set of values.

For more information about implementing your notification content app extension, see UNNotificationContentExtension Protocol Reference.

Presenting Notifications Using a Custom Interface on watchOS

The WatchKit framework provides direct support for presenting notifications using a custom interface. A WatchKit extension may include one or more notification interface controllers to display when notifications arrive for your app. You use these interface controllers to present the content of your notifications. For information on how to implement a notification interface controller, see App Programming Guide for watchOS.