Programming
Will iOS launch my app into the background if it was force-quit by the user
The behavior of iOS regarding background app launches after a user force-quits an application is a frequently debated topic among developers. Understanding whether iOS will launch my app into the background if it was force-quit by the user is crucial for designing efficient and reliable mobile applications. Force-quitting, or “killing” an app, signals to the operating system that the user intends to completely terminate the app’s processes. This action has significant implications for how iOS schedules and manages the app’s future background activities. This article dives deep into the nuances of iOS background app refresh, push notifications, and the impact of user-initiated force quits on your app’s lifecycle. We will explore the different scenarios and provide clarity on when and how iOS might relaunch your app, even after it has been explicitly terminated.
Understanding iOS App States and the App Lifecycle
iOS manages applications through a defined lifecycle, encompassing several states: Not Running, Inactive, Active, Background, and Suspended. When an app is force-quit by the user, it transitions directly to the Not Running state. This is a critical distinction because it signifies that the app is not actively in memory and will not execute any code unless explicitly launched again by the user or triggered by the system under specific circumstances. Understanding these states is essential for grasping how background tasks are handled. The app delegate methods, such as applicationDidEnterBackground: and applicationWillEnterForeground:, are key in managing the app’s behavior as it transitions between these states.
The core principle to remember is that iOS prioritizes battery life and system performance. Therefore, it’s designed to prevent apps from running indefinitely in the background without explicit user authorization or compelling reasons. Apple’s documentation emphasizes that apps should be designed to gracefully handle being terminated and relaunched. This means saving state, releasing resources, and being prepared to resume operations seamlessly when the user returns to the app. Failure to adhere to these guidelines can result in a poor user experience and potential rejection from the App Store.
Furthermore, the system’s behavior can change based on the user’s interaction with the app. For example, frequent force-quitting may signal to iOS that the user does not want the app running in the background, potentially affecting how aggressively the system allows it to be relaunched for background tasks. According to Apple’s developer guidelines, “The system does not automatically relaunch apps that are force quit by the user. When the user force quits an app, the system suspends all tasks and prevents the app from receiving any further background events. The app remains in this state until the user explicitly launches it again or the system needs to free up memory.” Apple Developer Documentation
The Impact of Force-Quitting on Background App Refresh
Background App Refresh (BAR) allows apps to periodically update their content in the background, providing a more seamless user experience. However, force-quitting an app significantly alters how BAR functions. While iOS typically schedules background refresh tasks based on usage patterns and system conditions, a force-quit effectively disables these scheduled tasks. The system interprets the force-quit as a clear signal that the user does not want the app running in the background, thus preventing BAR from occurring until the app is explicitly launched again by the user.
It’s important to note that BAR is also subject to user control via the Settings app. Users can disable BAR globally or on a per-app basis. Even if BAR is enabled, iOS intelligently manages its execution based on factors like battery life, network conditions, and app usage. The system will defer or prevent background refreshes if the device is in Low Power Mode or if the app has not been used recently. This intelligent management is further influenced by a force-quit, making it less likely for the app to receive background refresh opportunities.
Featured Snippet: If an iOS app is force-quit by the user, background app refresh is generally disabled. iOS interprets the force-quit as an indication that the user does not want the app running in the background. Consequently, the system will not schedule background refresh tasks for the app until the user manually relaunches it. This behavior is intended to respect the user’s explicit action of terminating the app and to conserve battery life.
Push Notifications and Background App Launch
Push notifications offer a pathway for iOS to potentially relaunch an app that has been force-quit, but the circumstances are specific. If a push notification contains the content-available key set to 1, it signals to iOS that the app should be launched in the background to handle the notification content. This is often used for silent push notifications, where the user is not explicitly alerted, but the app performs background processing, such as updating data or downloading content. However, even with content-available set, iOS may still not launch the app if it has been force-quit. The system considers the user’s explicit termination of the app as a strong signal to respect their preference.
It’s crucial to differentiate between regular push notifications and Voice over Internet Protocol (VoIP) push notifications. VoIP notifications are designed for apps that provide real-time communication services, such as phone calls or video conferencing. These notifications have a higher priority and are more likely to trigger a background launch, even after a force-quit. However, this is because VoIP apps are considered essential for maintaining communication services and are granted special privileges by iOS.
The key takeaway is that while push notifications can potentially trigger a background launch after a force-quit, it’s not guaranteed. The likelihood depends on the type of notification (silent vs. VoIP), the user’s behavior (frequency of force-quitting), and the overall system conditions. Developers should not rely solely on push notifications as a reliable mechanism for launching an app in the background after it has been explicitly terminated by the user. According to a study by Localytics, users who force-quit apps are less likely to engage with them in the future. Localytics App Abandonment Report
Geofencing and Location Updates
Geofencing and significant location updates provide another mechanism by which iOS might relaunch an app after it’s been force-quit, albeit under very specific circumstances. Geofencing allows an app to register regions of interest, and iOS will wake the app when the user enters or exits those regions. Similarly, significant location updates notify the app when the device detects a significant change in location. However, a force-quit significantly impacts the reliability of these mechanisms.
While iOS may still deliver geofencing or significant location updates to a force-quit app, it’s far less reliable than if the app were simply suspended in the background. The system prioritizes respecting the user’s explicit termination of the app. Furthermore, frequent force-quitting of an app can negatively impact the system’s willingness to relaunch it for location-based events. iOS learns from user behavior and adjusts its scheduling accordingly.
To optimize location-based functionality, developers should use the most efficient location-tracking techniques and minimize battery consumption. This includes using region monitoring judiciously and avoiding continuous location updates unless absolutely necessary. It’s also crucial to handle location updates gracefully and avoid performing intensive tasks in the background, as this can lead to the app being terminated by the system for excessive resource usage. Remember to check out this helpful resource for more tips.
Given the uncertainties surrounding background app launches after a force-quit, it’s essential to implement robust strategies for handling app termination and restoration. This includes properly saving app state, gracefully handling interruptions, and minimizing reliance on background tasks that may not execute reliably.
Here are some best practices to follow:
- Save App State: Implement the applicationWillTerminate: delegate method to save the app’s current state before termination. This allows the app to restore its previous state when relaunched, providing a seamless user experience.
- Handle Interruptions Gracefully: Design the app to gracefully handle interruptions, such as incoming phone calls or SMS messages. This ensures that the app can resume its operations smoothly after the interruption is handled.
Consider these steps for a smoother user experience:
- Implement state saving in applicationWillTerminate:.
- Use NSUserDefaults or Core Data for persistent storage.
- Test state restoration thoroughly.
By adhering to these best practices, developers can mitigate the negative impact of force-quitting and ensure a more resilient and user-friendly application. Remember that proactive design choices can greatly enhance the app’s ability to recover from unexpected terminations and maintain a positive user experience, even in the face of user-initiated force quits. According to Statista, the average smartphone user has around 80 apps installed, emphasizing the importance of a seamless user experience to retain engagement. Statista - Number of apps available
FAQ: Force-Quitting and iOS App Behavior
- Will my app always be prevented from running in the background if force-quit?
- Generally, yes. iOS treats force-quitting as a strong signal that the user wants the app completely terminated. Background App Refresh, geofencing, and other background tasks are less likely to be triggered.
- Can push notifications still launch my app if it was force-quit?
- Potentially, but not reliably. Silent push notifications (with content-available=1) have a chance, but iOS prioritizes the user's force-quit action. VoIP notifications have a higher chance of launching the app.
- Does frequent force-quitting affect background behavior?
- Yes. iOS learns from user behavior. Frequent force-quitting signals that the user doesn't want the app running in the background, making it less likely for the system to allow background tasks.
Here is the implementation I am using in my AppDelegate.m:
- (void)application:(UIApplication *)application didReceiveRemoteNotification:(NSDictionary *)userInfo fetchCompletionHandler:(void (^)(UIBackgroundFetchResult))completionHandler { NSLog(@"Remote Notification Recieved"); UILocalNotification *notification = [[UILocalNotification alloc] init]; notification.alertBody = @"Looks like i got a notification - fetch thingy"; [application presentLocalNotificationNow:notification]; completionHandler(UIBackgroundFetchResultNewData); }
When the app is running in the background, it works fine. (The notification is received and the app triggered the “looks like i got a notification” local notification, as the code above should do).
However, when the app is not running and a push notification is received with the content-available flag, the app is not launched and the didRecieveRemoteNotification delegate method is never called.
The WWDC Video Whats New With Multitasking (#204 from WWDC 2013) shows this: 
It says that the application is “launched into background” when a push notification is received with the content-available flag.
Why is my app not launching into the background?
So the real question is:
Will iOS perform background tasks after the user has force-quit the app?
UPDATE2:
You can achieve this using the new PushKit framework, introduced in iOS 8. Though PushKit is used for VoIP. So your usage should be for VoIP related otherwise there is risk of app rejection. (See this answer).
UDPDATE1:
The documentation has been clarified for iOS8. The documentation can be read here. Here is a relevant excerpt:
Use this method to process incoming remote notifications for your app. Unlike the
application:didReceiveRemoteNotification:method, which is called only when your app is running in the foreground, the system calls this method when your app is running in the foreground or background. In addition, if you enabled the remote notifications background mode, the system launches your app (or wakes it from the suspended state) and puts it in the background state when a push notification arrives. However, the system does not automatically launch your app if the user has force-quit it. In that situation, the user must relaunch your app or restart the device before the system attempts to launch your app automatically again.
Although this was not made clear by the WWDC video, a quick search on the developer forums turned this up:
https://devforums.apple.com/message/873265#873265 (login required)
Also keep in mind that if you kill your app from the app switcher (i.e. swiping up to kill the app) then the OS will never relaunch the app regardless of push notification or background fetch. In this case the user has to manually relaunch the app once and then from that point forward the background activities will be invoked. -pmarcos
That post was by an Apple employee so I think i can trust that this information is correct.
So it looks like when the app is killed from the app switcher (by swiping up), the app will never be launched, even for scheduled background fetches.
