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Pawel Rusin (@RusinPaw) iOS dev at Cookpad Tokyo iOS Meetup 2016-08-13 Background execution in iOS

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Agenda ● Motivation ● App lifecycle ● Background execution modes – App leaves the foreground – App enters the background – App enters the foreground ● Summary

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Motivation

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I want to make an app that does X

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I want to make an app that does X (In the background)

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How in iOS can I do X?

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How in iOS can I do X? (In the background)

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Is it OK in iOS to do X?

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Is it OK in iOS to do X? (In the background)

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https://developer.apple.com/app-store/review/rejections/

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How in iOS can I do X? (In the background)

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Google

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Stack overflow

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Google

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● What can be done? ● What cannot be done? ● What shouldn't be done?

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App lifecycle

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App lifecycle Inactive Active Background Foreground Background

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App lifecycle Not running Inactive Active Background Suspended Foreground Background

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App leaves the foreground

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Not running Inactive Active Background Suspended Foreground Background App leaves the foreground

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Executing Finite-Length Tasks

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Executing Finite-Length Tasks When the user is not actively using your app, the system moves it to the background state. For many apps, the background state is just a brief stop on the way to the app being suspended. Suspending apps is a way of improving battery life it also allows the system to devote important system resources to the new foreground app that has drawn the user’s attention. An app in the background state should do as little work as possible. Apps that request time to process specific types of events should process those events and return control back to the system as quickly as possible. App Programming Guide for iOS (background execution) UIAppDelegate documentation

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Executing Finite-Length Tasks When the user is not actively using your app, the system moves it to the background state. For many apps, the background state is just a brief stop on the way to the app being suspended. Suspending apps is a way of improving battery life it also allows the system to devote important system resources to the new foreground app that has drawn the user’s attention. An app in the background state should do as little work as possible. Apps that request time to process specific types of events should process those events and return control back to the system as quickly as possible. App Programming Guide for iOS (background execution) UIAppDelegate documentation

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Executing Finite-Length Tasks https://developer.apple.com/library/ios/documentation/UIKit/Reference/UIApplication_Class/index.html

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Executing Finite-Length Tasks Icon made by Silviu Runceanu from www.flaticon.com

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Executing Finite-Length Tasks Downloading Content in the Background App leaves the foreground

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App leaves the foreground UIApplication.sharedApplication().begi nBackgroundTaskWithExpirationHandler { // perform a finite tast } UIApplication().sharedApplic ation.endBackgroundTask()

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● Passes the download task to a separate process ● Requires specific type of NSURLSession – background session ● Gwendolyn Weston: “While Your App Was Sleeping: Background Transfer Services” Downloading Content in the Background

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App enters the background

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App enters the background Not running Inactive Active Background Suspended Foreground Background

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Audio and AirPlay Location updates Voice over IP Newsstand downloads External accessory communication Uses Bluetooth LE accessories Acts as a Bluetooth LE accessory Background fetch Remote notifications launch App enters the background

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App enters the background

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App enters the background trigger

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App enters the background trigger Audio buffer empty Location update Download task finished Time elapsed Silent push data from a peripheral

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Audio and AirPlay Location updates Voice over IP Newsstand downloads External accessory communication Uses Bluetooth LE accessories Acts as a Bluetooth LE accessory Background fetch Remote notifications launch App enters the background

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Audio and AirPlay Location updates Voice over IP Newsstand downloads External accessory communication Uses Bluetooth LE accessories Acts as a Bluetooth LE accessory Background fetch Remote notifications launch App enters the background

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● Apps that need to check for new content periodically can ask the system to wake them up so that they can initiate a fetch operation for that content. ● Enabling this mode is not a guarantee that the system will give your app any time to perform background fetches. ● The system must balance your app’s need to fetch content with the needs of other apps and the system itself. Background fetch https://developer.apple.com/library/ios/documentation/iPhone/Conceptual/iPhoneOSProgramming Guide/BackgroundExecution/BackgroundExecution.html

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Background fetch

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Background fetch UIApplication.sharedApplication().setMinimumBackgro undFetchInterval(24*60*60) (UIApplicationBackgroundFetchIntervalMinimum)

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Background fetch func application(application: UIApplication, performFetchWithCompletionHandler completionHandler: (UIBackgroundFetchResult) -> Void) { //fetch sth if error != nil { return completion(UIBackgroundFetchResultFailed) } else if newData { return completion(UIBackgroundFetchResultNewData) } else { return completion(UIBackgroundFetchResultNoData) } }

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Remote (silent) push { ... content-available: 1, ... }

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Remote (silent) push

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Remote (silent) push func application(application: UIApplication, didReceiveRemoteNotification userInfo: [NSObject : AnyObject]) { //do sth }

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● Specific tasks of a short execution time ● Know your API (and your limitations) ● Don't be greedy App enters the background

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App enters the foreground

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Not running Inactive Active Background Suspended App enters the foreground USER CONSENT

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Remote notifications Local Notification App enters the foreground

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App enters the foreground let localNotification = UILocalNotification() localNotification.fireDate = NSDate(timeIntervalSinceNow: 300) // 5mins localNotification.alertBody = "stand up!" localNotification.timeZone = NSTimeZone.defaultTimeZone() UIApplication.sharedApplication().scheduleLocalNotification(l ocalNotification)

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App enters the foreground func application(application: UIApplication, didReceiveLocalNotification notification: UILocalNotification) { //do sth }

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● One way of “reminding” user about the app ● Alarms, motivational apps ● Be nice! App enters the foreground

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● What can be done? ● What cannot be done? ● With great power comes great responsibility Summary

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● https://developer.apple.com/library/ios/documentation/iPhone/Co nceptual/iPhoneOSProgrammingGuide/BackgroundExecution/Ba ckgroundExecution.html ● https://developer.apple.com/library/ios/documentation/UIKit/Refer ence/UIApplicationDelegate_Protocol/ ● https://realm.io/news/gwendolyn-weston-ios-background- networking/ ● https://blog.newrelic.com/2016/01/13/ios9-background-execution/ References