How can an iOS app do work in the background?

#TL;DR

iOS suspends your app soon after it goes to the background. To keep working, pick the right tool:

The system decides when most tasks run. You cannot force exact times.

#1. Finish a short task

func sceneDidEnterBackground(_ scene: UIScene) {
    var taskID: UIBackgroundTaskIdentifier = .invalid
    taskID = UIApplication.shared.beginBackgroundTask(withName: "SaveDraft") {
        // Time is up. Clean up fast.
        UIApplication.shared.endBackgroundTask(taskID)
    }
    Task {
        await draftStore.save()
        UIApplication.shared.endBackgroundTask(taskID)
    }
}

You get a short time, often around 30 seconds. Always call endBackgroundTask, or the system may kill the app.

#2. BGTaskScheduler

Step 1: add the identifiers to Info.plist under BGTaskSchedulerPermittedIdentifiers, and turn on the "Background fetch" and/or "Background processing" modes.

Step 2: register before launch finishes.

import BackgroundTasks

func application(_ app: UIApplication,
                 didFinishLaunchingWithOptions options: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
    BGTaskScheduler.shared.register(forTaskWithIdentifier: "com.example.refresh", using: nil) { task in
        self.handleRefresh(task as! BGAppRefreshTask)
    }
    return true
}

Step 3: schedule and handle it.

func scheduleRefresh() {
    let request = BGAppRefreshTaskRequest(identifier: "com.example.refresh")
    request.earliestBeginDate = Date(timeIntervalSinceNow: 15 * 60)
    try? BGTaskScheduler.shared.submit(request)
}

func handleRefresh(_ task: BGAppRefreshTask) {
    scheduleRefresh() // schedule the next one
    let work = Task {
        let ok = await feedStore.refresh()
        task.setTaskCompleted(success: ok)
    }
    task.expirationHandler = { work.cancel() }
}

• BGAppRefreshTask: about 30 seconds. Runs based on how often the user opens the app.
• BGProcessingTask: minutes. Often at night while charging. Can require network or power.

SwiftUI has a modifier: .backgroundTask(.appRefresh("com.example.refresh")) { await refresh() }.

#3. Background URLSession

let config = URLSessionConfiguration.background(withIdentifier: "com.example.downloads")
config.isDiscretionary = true  // let the system pick a good time (Wi-Fi, charging)
let session = URLSession(configuration: config, delegate: self, delegateQueue: nil)
session.downloadTask(with: videoURL).resume()

The transfer runs in a system process. It continues if your app is suspended or even terminated by the system. When it finishes, iOS relaunches your app and calls application(_:handleEventsForBackgroundURLSession:completionHandler:). Use delegates, not async methods, with background sessions.

#4. BGContinuedProcessingTask (iOS 26)

For work the user started, like exporting a video. The system shows a progress UI, and the task keeps running after the user leaves the app. You must report progress, or the system may stop it.

#5. Silent push

A push with "content-available": 1 and no alert wakes the app for about 30 seconds. The system limits how often. Do not rely on it for every message.

#6. Background modes

Turned on in Signing & Capabilities. Each needs a real reason, or App Review rejects it:

• Audio: music and podcast playback.
• Location updates: navigation, fitness tracking.
• Voice over IP: with CallKit and PushKit.
• External accessory / Bluetooth: talk to devices.

#Testing tip

In the debugger, you can trigger a scheduled task:

e -l objc -- (void)[[BGTaskScheduler sharedScheduler] _simulateLaunchForTaskWithIdentifier:@"com.example.refresh"]

#Common follow-up questions

• Why does my background task never run? Not registered before launch ended, missing Info.plist identifier, Low Power Mode, or the user rarely opens the app.
• What if the user force-quits the app? Background refresh and silent pushes stop until the user opens the app again.
• Can a timer run in the background? No. Timers stop when the app is suspended.
• How do you save battery? Use isDiscretionary, batch work, and require power for heavy processing tasks.