Introduction

Silent push notifications are a powerful tool that allows apps to perform background actions without alerting the user directly. They are typically used for background content updates, refreshing app data quietly, or collecting usage analytics. However, with iOS 11, many developers encountered issues with silent pushes not being delivered to their apps, or not behaving as expected, which impacted user experience and app performance.

Understanding Silent Push Notifications

A silent push notification is sent to the user’s device without causing any visible alert or sound. Its primary goal is to wake up the app in the background to perform a task, such as downloading content. This functionality is essential for maintaining a seamless user experience, especially for apps that rely on fresh content.

Key Characteristics:

• No Alert or Sound: Users are not notified; the notification is handled silently.
• Background Execution: Invokes app background refresh without bringing the app to the foreground.
• Efficiency: Minimizes the power and data usage as compared to regular push notifications.

Issues with iOS 11

With the release of iOS 11, developers noticed that silent push notifications were not reliably reaching their apps. The reasons can be traced back to several changes Apple made regarding how background tasks and notifications are handled. Here’s a deeper look into the contributing factors:

Changes in Background Execution

iOS 11 introduced stricter controls on background execution to enhance battery life and overall system performance. These changes had direct implications on the delivery of silent push notifications:

• Background App Refresh: Previously, apps could maintain persistent background activities, but under iOS 11, these abilities were restricted. If an app is terminated, it might not receive silent pushes as expected.
• App States: Silent pushes only work efficiently if the app is in a suspended state but not if it has been manually terminated by the user.

Network Availability and Conditions

Another crucial factor affecting silent push delivery is network availability and conditions:

• Transient Connections: If the device is in a low connectivity area or switched to flight mode, silent pushes may fail to be delivered.
• Data Saver Modes: With data-saving features turned on, background processes, including silent push delivery, might be limited.

Server Configurations and Payload Size

There are also server-side and configuration aspects to be cognizant of:

• Payload Size: The payload for a silent push should not exceed 4 KB. Larger payloads might be rejected by the APNs (Apple Push Notification service).
• Content-Available Flag: The payload must include "content-available": 1 to signal the operating system to initiate a background download operation.

Mitigating Delivery Issues

To improve the reliability of silent push notifications on iOS 11, developers can adopt several strategies:

Optimize App Configuration

• Enable Background Modes: Ensure that background app refresh is enabled under capabilities in Xcode, and the necessary permissions are granted by the user.
• Use Remote Notification Key: In the Info.plist , add the UIBackgroundModes key with remote-notification to specify your app can receive silent push notifications.

Server-Side Adjustments

• Send Test Pushes: Regularly test the delivery of silent pushes across different network conditions and app states.
• Optimize Payload Content: Keep payload size minimal, strictly adhering to Apple’s 4 KB limit.

Alternate Solutions

• Local Notifications: For some use-cases, consider using local notifications to keep the app’s content fresh while providing users more control.

Conclusion

The challenges associated with silent pushes not being delivered on iOS 11 can be frustrating, but they underscore the importance of adapting to platform updates and optimizing application performance within new constraints. By understanding the intricacies of iOS 11's background execution policies and adjusting both client-side and server-side mechanisms, developers can ensure a more reliable experience for users.

Summary Table

Developers should consistently monitor Apple's updates on push notification services and background execution policies to be proactive in optimizing their applications.