Reloading a Displayed Page Automatically When a Background App Becomes Active in an iPhone Application with Phonegap/Cordova

As mobile applications continue to become more complex, the need for robust and efficient communication between different apps on the same device grows. In this article, we will explore how to reload a displayed page automatically when a background app becomes active in an iPhone application built with Phonegap/Cordova.

Introduction to Background Apps and Their Activation

In iOS, a background app is an application that continues to run even after it is no longer visible or has been sent to the background. This allows the app to continue performing tasks in the background, such as syncing data or updating the device’s location.

When a background app becomes active again, its icon appears on the home screen, and users can interact with it as they would any other app. However, this also means that the app is now visible again, and we may need to update the displayed page to reflect the changes made in the background.

Understanding Notifications in iOS

To achieve our goal of reloading a displayed page automatically when a background app becomes active, we can use the notification observer pattern. In iOS, notifications are used to communicate between apps or to notify the system of an event that requires attention.

Notifications are sent using the UIApplicationDidBecomeActiveNotification name, which is triggered when the user taps on an app’s icon after it has been sent to the background.

Registering for Notifications in a Phonegap/Cordova App

To register for this notification, we need to add an observer to our main view controller. We can do this by calling [super viewDidLoad] and then using the addObserver:selector:name.object: method of the NSNotificationCenter.

Here is an example:

- (void)viewDidLoad {
    [super viewDidLoad];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidBecomeActive:) name:UIApplicationDidBecomeActiveNotification object:nil];
}

In this code, we are registering ourself as an observer for the notification with the specified selector method. The object:nil argument tells iOS that there is no associated object with which to send the notification.

Implementing the Notification Observer Method

Once we have registered for the notification, we need to implement a method that will be called when the notification is sent. This method should contain the code that will reload our displayed page.

Here is an example:

- (void)appDidBecomeActive:(NSNotification *)notification {
    NSLog(@"App became active");
    // Reload your displayed page here, for example:
    [self reloadingDisplayedPage];
}

- (void)loadingDisplayedPage {
    // Your code to reload the displayed page goes here
}

In this code, we are implementing a method called appDidBecomeActive: that will be called when the notification is sent. Inside this method, we can add our own code to reload our displayed page.

Removing Observers When Necessary

When our view controller is deallocated (i.e., it is no longer needed), we should remove all observers for notifications. This ensures that we do not receive duplicate notifications and prevents potential memory leaks.

Here is an example:

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    NSLog(@"Removed all notification observers");
}

In this code, we are removing ourself as an observer for the UIApplicationDidBecomeActiveNotification when our view controller is deallocated.

Putting It All Together

To put it all together, here is a complete example:

// MainViewController.m

- (void)viewDidLoad {
    [super viewDidLoad];

    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(appDidBecomeActive:) name:UIApplicationDidBecomeActiveNotification object:nil];
}

- (void)appDidBecomeActive:(NSNotification *)notification {
    NSLog(@"App became active");
    [self reloadingDisplayedPage];
}

- (void)loadingDisplayedPage {
    // Your code to reload the displayed page goes here
    // For example:
    [self performSelector:@selector(reloadPage)];
}

- (void)reloadPage {
    // Reload your displayed page here, for example:
    self.displayedPage = [[UIView alloc] initWithFrame:self.view.frame];
    [self.view addSubview:self.displayedPage];
}

- (void)dealloc {
    [[NSNotificationCenter defaultCenter] removeObserver:self];
    NSLog(@"Removed all notification observers");
}

In this code, we are registering for the UIApplicationDidBecomeActiveNotification when our view controller is loaded. When this notification is sent, we call our appDidBecomeActive: method to reload our displayed page.

Conclusion

Reloading a displayed page automatically when a background app becomes active in an iPhone application with Phonegap/Cordova can be achieved using the notification observer pattern. By registering for notifications and implementing a method that will be called when these notifications are sent, we can ensure that our displayed page is always up to date.

This technique can be used in a variety of situations, such as when working with background apps or when you need to update your application’s UI in response to external events. With this knowledge, you should be able to implement this functionality in your own iPhone applications.

Last modified on 2025-03-24