background-processing

name background-processing description Schedule and execute background work on iOS using BGTaskScheduler. Use when registering BGAppRefreshTask for short background fetches, BGProcessingTask for long-running maintenance, BGContinuedProcessingTask (iOS 26+) for foreground-started work that continues in background, background URLSession downloads, or background push notifications. Covers Info.plist configuration, expiration handling, task completion, and debugging with simulated launches. Background Processing Register, schedule, and execute background work on iOS using the BackgroundTasks framework, background URLSession, and background push notifications. Contents Info.plist Configuration BGTaskScheduler Registration BGAppRefreshTask Patterns BGProcessingTask Patterns BGContinuedProcessingTask (iOS 26+) Background URLSession Downloads Background Push Triggers Common Mistakes Review Checklist References Info.plist Configuration Every task identifier must be declared in Info.plist under BGTaskSchedulerPermittedIdentifiers , or submit(_:) throws BGTaskScheduler.Error.Code.notPermitted . < key > BGTaskSchedulerPermittedIdentifiers </ key > < array > < string > com.example.app.refresh </ string > < string > com.example.app.db-cleanup </ string > < string > com.example.app.export.* </ string > </ array > Also enable the required UIBackgroundModes : < key > UIBackgroundModes </ key > < array > < string > fetch </ string > <!-- Required for BGAppRefreshTask --> < string > processing </ string > <!-- Required for BGProcessingTask --> </ array > In Xcode: target > Signing & Capabilities > Background Modes > enable "Background fetch" and "Background processing". BGTaskScheduler Registration Register handlers before app launch completes. In UIKit, register in application(_:didFinishLaunchingWithOptions:) ; in SwiftUI, register in App.init() . UIKit Registration import BackgroundTasks @main class AppDelegate : UIResponder , UIApplicationDelegate { func application ( _ application : UIApplication , didFinishLaunchingWithOptions launchOptions : [ UIApplication . LaunchOptionsKey : Any ] ? ) -> Bool { BGTaskScheduler .shared.register( forTaskWithIdentifier: "com.example.app.refresh" , using: nil // nil = default background queue ) { task in self .handleAppRefresh(task: task as! BGAppRefreshTask ) } BGTaskScheduler .shared.register( forTaskWithIdentifier: "com.example.app.db-cleanup" , using: nil ) { task in self .handleDatabaseCleanup(task: task as! BGProcessingTask ) } return true } } SwiftUI Registration import SwiftUI import BackgroundTasks @main struct MyApp : App { init () { BGTaskScheduler .shared.register( forTaskWithIdentifier: "com.example.app.refresh" , using: nil ) { task in BackgroundTaskManager .shared.handleAppRefresh( task: task as! BGAppRefreshTask ) } } var body: some Scene { WindowGroup { ContentView () } } } BGAppRefreshTask Patterns Short-lived tasks (~30 seconds) for fetching small data updates. The system decides when to launch; earliestBeginDate is only a lower-bound hint. func scheduleAppRefresh () { let request = BGAppRefreshTaskRequest ( identifier: "com.example.app.refresh" ) request.earliestBeginDate = Date (timeIntervalSinceNow: 15 * 60 ) do { try BGTaskScheduler .shared.submit(request) } catch { print ( "Could not schedule app refresh: \(error) " ) } } func handleAppRefresh ( task : BGAppRefreshTask ) { // Schedule the next refresh before doing work scheduleAppRefresh() let fetchTask = Task { do { let data = try await APIClient .shared.fetchLatestFeed() await FeedStore .shared.update(with: data) task.setTaskCompleted(success: true ) } catch { task.setTaskCompleted(success: false ) } } // CRITICAL: Handle expiration -- system can revoke time at any moment task.expirationHandler = { fetchTask.cancel() task.setTaskCompleted(success: false ) } } BGProcessingTask Patterns Long-running tasks (minutes) for maintenance, data processing, or cleanup. They run while the device is idle and can require external power; the same earliestBeginDate lower-bound rule applies. func scheduleProcessingTask () { let request = BGProcessingTaskRequest ( identifier: "com.example.app.db-cleanup" ) request.requiresNetworkConnectivity = false request.requiresExternalPower = true request.earliestBeginDate = Date (timeIntervalSinceNow: 60 * 60 ) do { try BGTaskScheduler .shared.submit(request) } catch { print ( "Could not schedule processing task: \(error) " ) } } func handleDatabaseCleanup ( task : BGProcessingTask ) { scheduleProcessingTask() let cleanupTask = Task { do { try await DatabaseManager .shared.purgeExpiredRecords() try await DatabaseManager .shared.rebuildIndexes() task.setTaskCompleted(success: true ) } catch { task.setTaskCompleted(success: false ) } } task.expirationHandler = { cleanupTask.cancel() task.setTaskCompleted(success: false ) } } BGContinuedProcessingTask (iOS 26+) A task initiated in the foreground by a user action that continues running in the background. The system displays progress via a Live Activity. Conforms to ProgressReporting . Availability: iOS 26.0+, iPadOS 26.0+ Unlike BGAppRefreshTask and BGProcessingTask , this task starts immediately from the foreground. The system can terminate it under resource pressure, prioritizing tasks that report minimal progress first. Set expirationHandler for user or system cancellation, cancel in-flight work, and clean up partial output before reporting completion. import BackgroundTasks func startExport () { // Register the task handler at app launch, not here. // BGTaskScheduler requires registration before app launch completes. let jobID = UUID ().uuidString let request = BGContinuedProcessingTaskRequest ( identifier: "com.example.app.export. \(jobID) " , title: "Exporting Photos" , subtitle: "Processing 247 items" ) // Use a permitted base wildcard identifier: com.example.app.export.* // earliestBeginDate is ignored for continued processing requests. // .queue: begin as soon as possible if can't run immediately // .fail: fail submission if can't run immediately request.strategy = .queue do { try BGTaskScheduler .shared.submit(request) } catch { print ( "Could not submit continued processing task: \(error) " ) } } func performExport ( task : BGContinuedProcessingTask ) async { let items = await PhotoLibrary .shared.itemsToExport() let progress = task.progress progress.totalUnitCount = Int64 (items.count) for (index, item) in items.enumerated() { if Task .isCancelled { break } await PhotoExporter .shared.export(item) progress.completedUnitCount = Int64 (index + 1 ) // Update the user-facing title/subtitle task.updateTitle( "Exporting Photos" , subtitle: " \(index + 1 ) of \(items.count) complete" ) } task.setTaskCompleted(success: ! Task .isCancelled) } For GPU work, check support and enable Background GPU Access ( com.apple.developer.background-tasks.continued-processing.gpu ): let supported = BGTaskScheduler .supportedResources if supported.contains(.gpu) { request.requiredResources = .gpu } Background URLSession Downloads Use URLSessionConfiguration.background for downloads that continue even after the app is suspended or terminated. The system handles the transfer out of process. class DownloadManager : NSObject , URLSessionDownloadDelegate { static let shared = DownloadManager () private lazy var session: URLSession = { let config = URLSessionConfiguration .background( withIdentifier: "com.example.app.background-download" ) config.isDiscretionary = true config.sessionSendsLaunchEvents = true return URLSession (configuration: config, delegate: self , delegateQueue: nil ) }() func startDownload ( from url : URL ) { let task = session.downloadTask(with: url) task.earliestBeginDate = Date (timeIntervalSinceNow: 60 ) task.resume() } func urlSession ( _ session : URLSession , downloadTask : URLSessionDownloadTask , didFinishDownloadingTo location : URL ) { // Move file from tmp before this method returns let dest = FileManager .default.urls( for: .documentDirectory, in: .userDomainMask )[ 0 ].appendingPathComponent( "download.dat" ) try? FileManager .default.moveItem(at: location, to: dest) } func urlSession ( _ session : URLSession , task : URLSessionTask , didCompleteWithError error : ( any Error ) ? ) { if let error { print ( "Download failed: \(error) " ) } } } Handle app relaunch — store and invoke the system completion handler: // In AppDelegate: func application ( _ application : UIApplication , handleEventsForBackgroundURLSession identifier : String , completionHandler : @escaping () -> Void ) { backgroundSessionCompletionHandler = completionHandler } // In URLSessionDelegate — call stored handler when events finish: func urlSessionDidFinishEvents ( forBackgroundURLSession session : URLSession ) { Task { @MainActor in self .backgroundSessionCompletionHandler ? () self .backgroundSessionCompletionHandler = nil } } Background Push Triggers Silent push notifications wake your app briefly to fetch new content. Set content-available: 1 in the push payload. { "aps" : { "content-available" : 1 } , "custom-data" : "new-messages" } Send the APNs request with apns-push-type: background and apns-priority: 5 . Background push delivery is low priority and not guaranteed; keep sends infrequent, generally no more than two or three per hour. Handle in AppDelegate: func application ( _ application : UIApplication , didReceiveRemoteNotification userInfo : [ AnyHashable : Any ], fetchCompletionHandler completionHandler : @escaping ( UIBackgroundFetchResult ) -> Void ) { Task { do { let hasNew = try await MessageStore .shared.fetchNewMessages() completionHandler(hasNew ? .newData : .noData) } catch { completionHandler(.failed) } } } Enable "Remote notifications" in Background Modes and register: UIApplication .shared.registerForRemoteNotifications() Common Mistakes 1. Missing Info.plist identifiers // DON'T: Submit a task whose identifier isn't in BGTaskSchedulerPermittedIdentifiers let request = BGAppRefreshTaskRequest (identifier: "com.example.app.refresh" ) try BGTaskScheduler .shared.submit(request) // Throws .notPermitted // DO: Add every identifier to Info.plist BGTaskSchedulerPermittedIdentifiers // <string>com.example.app.refresh</string> 2. Not calling setTaskCompleted(success:) Use the canonical app-refresh or processing handler above: every success, failure, and cancellation path reports completion exactly once. 3. Ignoring the expiration handler Use the same canonical handler to cancel in-flight work and report failure from expirationHandler . 4. Scheduling too frequently The scheduling sections own the lower-bound rule. Avoid minute-scale refresh requests; the system still chooses actual launch time. 5. Over-relying on background time // DON'T: Start a 10-minute operation assuming it will finish func handleRefresh ( task : BGAppRefreshTask ) { Task { await tenMinuteSync() } } // DO: Design work to be incremental and cancellable func handleRefresh ( task : BGAppRefreshTask ) { let work = Task { for batch in batches { try Task .checkCancellation() await processBatch(batch) await saveBatchProgress(batch) } task.setTaskCompleted(success: true ) } task.expirationHandler = { work.cancel() task.setTaskCompleted(success: false ) } } Review Checklist All task identifiers listed in BGTaskSchedulerPermittedIdentifiers Required UIBackgroundModes enabled ( fetch , processing ) Tasks registered before app launch completes setTaskCompleted(success:) called on every code path expirationHandler set and cancels in-flight work Next task scheduled inside the handler (re-schedule pattern) earliestBeginDate uses reasonable intervals and is treated as a hint Background URLSession uses delegate (not async/closures) Background URLSession file moved in didFinishDownloadingTo before return handleEventsForBackgroundURLSession stores and calls completion handler Background push payload includes content-available: 1 Background push APNs request uses apns-push-type: background and apns-priority: 5 fetchCompletionHandler called promptly with correct result BGContinuedProcessingTask reports progress via ProgressReporting Work is incremental and cancellation-safe ( Task.checkCancellation() ) No blocking synchronous work in task handlers References See references/background-task-patterns.md for extended patterns, background URLSession edge cases, debugging with simulated launches, and background push best practices. BGTaskScheduler BGAppRefreshTask BGProcessingTask BGContinuedProcessingTask (iOS 26+) BGContinuedProcessingTaskRequest (iOS 26+) Using background tasks to update your app Performing long-running tasks on iOS and iPadOS