Understanding Background App Refresh in iOS 7

Understanding Background App Refresh in iOS

Introduction

Background App Refresh (BAR) is a feature introduced in iOS 7 that allows apps to continue running and refreshing their data even when they are not currently active. This feature has been a subject of interest for many developers, as it can be both a blessing and a curse. In this article, we will explore the concept of BAR, its history, and how it is implemented in iOS 7.

History of Background App Refresh

BAR was first introduced in iOS 3.0, but it was limited to only a few apps that were explicitly allowed by Apple. Over time, Apple expanded the list of eligible apps, but it still required developers to request permission from their users before they could enable BAR for their app.

In iOS 7, Apple completely overhauled the way BAR worked. Now, any app can opt-in to BAR, and it is enabled by default in most cases. However, this also means that if an app’s background process crashes or becomes unresponsive, it will not restart automatically like it did on older versions of iOS.

How Background App Refresh Works

So, how does BAR work? When you run an app with BAR enabled, the operating system (OS) creates a separate process for the app’s background activity. This process is called the “background task” or “system background task.”

When the OS detects that an app has been launched and is in the background, it will schedule a series of tasks to be executed by the background process. These tasks are typically related to network communication, file access, or other activities that need to continue even when the app is not active.

If the background process crashes or becomes unresponsive, the OS will detect this and terminate the task. However, unlike older versions of iOS, the OS will not restart the entire app. Instead, it will allow the app to recover from the crash by reloading its state and resuming its activities.

What’s Different about iOS 7

So, what’s different about how BAR works on iOS 7 compared to earlier versions? In iOS 6 and earlier, when an app’s background process crashed, the OS would restart the entire app. This was because the OS had a harder time determining which specific part of the app had caused the crash.

In iOS 7, Apple changed its approach by introducing a new system called “Background Task Completion.” When an app’s background task completes successfully, it is reported back to the OS as a success. However, if the task crashes or becomes unresponsive, it is reported as a failure.

This change allows the OS to better determine which specific part of the app caused the crash and restart that component instead of the entire app.

Why Doesn’t My App Restart When It Crashes?

So, why doesn’t my app restart when it crashes in iOS 7? There are several reasons for this:

Background Task Completion: As mentioned earlier, iOS 7 introduces a new system called “Background Task Completion.” This system allows the OS to better determine which specific part of the app caused the crash and restart that component instead of the entire app.
App Sandbox: In iOS 7, apps are running in a sandboxed environment. This means that each app has its own isolated space for storing data, communicating with other apps, and accessing system resources. When an app crashes, it is terminated from this sandboxed environment, but its data remains intact.

By allowing the OS to detect which specific component of the app crashed and restarting only that component, iOS 7 prevents the entire app from restarting unnecessarily. However, this also means that if an app’s background process crashes or becomes unresponsive, it will not restart automatically like it did on older versions of iOS.

Conclusion

Background App Refresh is a powerful feature in iOS 7 that allows apps to continue running and refreshing their data even when they are not currently active. While this feature can be both beneficial and frustrating for developers, understanding how it works is essential for building robust and reliable apps.

In conclusion, the reason why my app does not restart when it crashes on iOS 7 is due to the new system of Background Task Completion introduced in iOS 7. This system allows the OS to better determine which specific part of the app caused the crash and restart that component instead of the entire app.

Additional Resources

Apple Developer Documentation: Background Tasks
Apple Developer Documentation: [App Sandbox](https://developer.apple.com/library/archive/documentation/General/Conceptual/AppleHIG Guides/iPhoneOS/Introduction/Introduction.html#//apple_ref/doc/uid/TP40004514-101208)
Stack Overflow Discussion: How to make my app restart when it crashes in background on iOS 7

Last modified on 2023-08-04