Background Processing
Register, schedule, and execute background work on iOS using the BackgroundTasks
framework, background URLSession, and background push notifications.
Contents
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
References
anthropics/skills180k
