Understanding Background Execution in iOS

In a typical iOS application, background execution is used to perform tasks that are not directly related to the user interface, such as fetching data from remote servers, processing large amounts of data, or sending notifications. In this article, we will explore how to run classes in the background on an iOS device.

Understanding Background Execution

Background execution on iOS is made possible through a combination of features and guidelines set by Apple. The iOS operating system provides several mechanisms for executing tasks in the background, including:

• Background Tasks: These are tasks that can be executed while the app is running in the foreground, but not when it’s suspended or terminated.
• Remote Notifications: These allow an app to send notifications to users even when the app is not running.
• Location Services: This feature allows apps to access a device’s location data, which can be used for various purposes such as tracking a user’s movement.

Understanding Multithreaded Programming

Before we dive into background execution, it’s essential to understand multithreaded programming. In multithreaded programming, multiple threads (or streams of execution) are executed concurrently within the same process. This allows an app to perform multiple tasks simultaneously, improving overall system responsiveness and efficiency.

However, this also introduces a new challenge: coordinating the execution of these threads to ensure data consistency and prevent deadlocks.

Apple’s Guidelines for Background Execution

Apple provides guidelines for background execution in its documentation:

• Background Tasks: Apps can request background execution on a specific task type (e.g., fetch, update, or send). However, this requires a valid reason for the app to access data during background time.
• Remote Notifications: These notifications are displayed when an app is not running. This allows users to receive updates even when the app is suspended or terminated.

Sample Code: Background Execution with Remote Notifications

Let’s create a simple example that demonstrates how to use remote notifications for background execution:

First, we need to add our app’s notification settings in our Info.plist file:

<key>UIBackgroundModes</key>
<array>
    <string>fetch-data</string>
    <string>remote-notification</string>
</array>

Next, create a service class that handles background data fetching and remote notifications:

import Foundation

class BackgroundService {
    
    static func fetchData() {
        // Implement your data fetching logic here.
        print("Background: Fetching data...")
    }
    
    static func handleRemoteNotification(_ notification: Notification) {
        // Implement your remote notification handling logic here.
        print("Background: Received remote notification!")
        
        // Post a local notification to notify the user
        let center = UNUserNotificationCenter.current()
        center.postNotification(UNNotificationContent(), withCompletionHandler: nil)
    }
}

In this example, we’re requesting background execution on both fetch-data and remote-notification task types. When our app is running in the foreground, it will execute these tasks concurrently.

However, for remote notifications, we need to handle them when the app is not running. This can be done by implementing the handleRemoteNotification(_:) function, which is called when a remote notification is received.

iOS 14+ Background Tasks with User Notifications

Starting from iOS 14, Apple introduced background tasks with user notifications. These allow an app to send local notifications to users even while the app is running in the background.

Here’s how you can modify our example to use background tasks with user notifications:

First, we need to add our app’s notification settings in our Info.plist file:

<key>UIBackgroundModes</key>
<array>
    <string>fetch-data</string>
    <string>remote-notification</string>
</array>

<key>AppGroups</key>
<string>group.com.yourcompany.backgroundshare</string>

Next, create a service class that handles background data fetching and user notifications:

import Foundation

class BackgroundService {
    
    static func fetchData() {
        // Implement your data fetching logic here.
        print("Background: Fetching data...")
        
        // Post a local notification to notify the user
        let center = UNUserNotificationCenter.current()
        center.postNotification(UNNotificationContent(), withCompletionHandler: nil)
    }
    
    static func handleRemoteNotification(_ notification: Notification) {
        // Implement your remote notification handling logic here.
        print("Background: Received remote notification!")
        
        // Post a local notification to notify the user
        let center = UNUserNotificationCenter.current()
        center.postNotification(UNNotificationContent(), withCompletionHandler: nil)
    }
}

In this example, we’re requesting background execution on both fetch-data and remote-notification task types. When our app is running in the foreground, it will execute these tasks concurrently.

However, for remote notifications, we need to handle them when the app is not running. This can be done by implementing the handleRemoteNotification(_:) function, which is called when a remote notification is received.

Conclusion

In this article, we explored how to run classes in the background on an iOS device. We discussed Apple’s guidelines for background execution and provided examples of how to use remote notifications and background tasks with user notifications.

Remember to always follow best practices for multithreaded programming and handle potential errors when working with background execution.

Last modified on 2025-02-15