Understanding the Behavior of UIViewController Lifecycle Methods: ViewDidAppear is Not Called When Opening App from Background

28 February 2025 Stephan Petzl Leave a comment Xcode

The lifecycle of a UIViewController can sometimes be perplexing, especially when dealing with app transitions from the background to the foreground. A common issue developers face is that viewDidAppear is not triggered when reopening an app from the background. This article will guide you through understanding this behavior and how to effectively manage it.

Why viewDidAppear May Not Be Called

When an app is reopened from the background, the system does not call viewDidAppear or viewWillAppear automatically. This is because these methods are part of the view controller’s lifecycle which is only triggered during transitions initiated by the app itself, not by system-level transitions such as app backgrounding.

Solution: Using Notifications to Handle App Transitions

To manage the transition from background to foreground, you can use the NSNotificationCenter to observe specific notifications that inform you when the app becomes active again. Here’s a step-by-step guide on how to implement this:

Objective-C Implementation

- (void)viewDidLoad {
    [super viewDidLoad];
    [[NSNotificationCenter defaultCenter] addObserver:self 
                                             selector:@selector(appDidBecomeActive:) 
                                                 name:UIApplicationDidBecomeActiveNotification 
                                               object:nil];
}

- (void)appDidBecomeActive:(NSNotification *)notification {
    // Update your UI or perform required actions
}

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
}
  

Swift Implementation

override func viewDidLoad() {
    super.viewDidLoad()
    NotificationCenter.default.addObserver(self, 
                                           selector: #selector(appDidBecomeActive), 
                                           name: UIApplication.didBecomeActiveNotification, 
                                           object: nil)
}

@objc func appDidBecomeActive() {
    // Update your UI or perform required actions
}

deinit {
    NotificationCenter.default.removeObserver(self)
}
  

Practical Considerations

While implementing this solution, ensure that you only perform actions that need to be updated when the app becomes active again. This approach allows you to maintain a responsive and up-to-date user interface.

Enhancing Test Automation with Repeato

When developing and testing your app, ensuring that the app’s behavior is consistent and reliable when transitioning from background to foreground is crucial. Using automated testing tools like Repeato can significantly streamline this process. Repeato is a no-code test automation tool that allows you to record and run tests efficiently using computer vision and AI. It supports data-driven testing and integrates easily with version control systems, ensuring your tests are as dynamic and adaptable as your app itself.

Unlike other tools, Repeato eliminates the need for scripting in Groovy (Java) and supports a wide range of testing needs without requiring paid licenses for advanced features. This makes it a practical alternative, particularly for developers looking for a flexible and cost-effective solution.

For more information on using Repeato for test automation, feel free to check our documentation or contact us for support.

Check it out!

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