How to Detect If an App Has Been Backgrounded Using AppDelegate

In this article, we'll explore how to detect if an app has been backgrounded using the AppDelegate class. We'll walk through the necessary steps to achieve this and provide some code examples to make it easier to follow.

Step 1: Set up the delegate methods

The first step in detecting if an app has been backgrounded is to set up the necessary delegate methods in the AppDelegate class. These methods are called by the system when certain events occur, such as when the app is launched or when it enters the background.

The two delegate methods we need to implement are:

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1func applicationDidEnterBackground(_ application: UIApplication) {
2    // App entered background
3}
4
5func applicationWillEnterForeground(_ application: UIApplication) {
6    // App will enter foreground
7}

The applicationDidEnterBackground method is called when the app enters the background, and the applicationWillEnterForeground method is called when the app is about to enter the foreground again. We can use these methods to detect when the app has been backgrounded and when it's about to come back to the foreground.

Step 2: Use flags to track the app state

The second step is to use flags to track the app's state. We can create a boolean variable called isInBackground and set it to false initially. When the app enters the background, we can set this variable to true, and when it comes back to the foreground, we can set it back to false.

Here's an example implementation:

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1class AppDelegate: UIResponder, UIApplicationDelegate {
2
3    var isInBackground = false
4
5    func applicationDidEnterBackground(_ application: UIApplication) {
6        isInBackground = true
7    }
8
9    func applicationWillEnterForeground(_ application: UIApplication) {
10        isInBackground = false
11    }
12
13    // ...
14}

Step 3: Use the flag to detect the app state

The final step is to use the isInBackground flag to detect the app's state. We can use this flag to perform certain actions when the app is in the background, such as pausing a game or stopping an audio player.

Here's an example implementation:

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1class ViewController: UIViewController {
2
3    let audioPlayer = AVAudioPlayer()
4
5    override func viewDidLoad() {
6        super.viewDidLoad()
7
8        let url = URL(fileURLWithPath: Bundle.main.path(forResource: "music", ofType: "mp3")!)
9        audioPlayer = try! AVAudioPlayer(contentsOf: url)
10        audioPlayer.prepareToPlay()
11    }
12
13    override func viewDidAppear(_ animated: Bool) {
14        super.viewDidAppear(animated)
15
16        if let appDelegate = UIApplication.shared.delegate as? AppDelegate {
17            if appDelegate.isInBackground {
18                // App is in the background, stop the audio player
19                audioPlayer.stop()
20            } else {
21                // App is in the foreground, start the audio player
22                audioPlayer.play()
23            }
24        }
25    }
26
27    // ...
28}

In this example, we're using the isInBackground flag to determine whether the app is in the background or foreground. If it's in the background, we stop the audio player, and if it's in the foreground, we start the audio player.

Conclusion

Detecting if an app has been backgrounded is an essential part of iOS development. By using the AppDelegate delegate methods and flags, we can easily detect when an app has been backgrounded and perform the necessary actions to ensure that the app behaves consistently and responsively. With these steps in mind, you can easily detect when your app has been backgrounded and customize its behavior accordingly.

In addition to the examples provided above, there are many other ways to detect when your app has been backgrounded. For instance, you can use the NotificationCenter to register for specific events and receive notifications when the app enters the background or foreground. You can also use the UIApplicationState property to check the app's state directly.