Which UIViewController method is called when an application is opened from the background?

Question

Is there any convenient way to determine if a view is loading from an application in the background?

In 3.X, I would rely on viewDidLoad to do the initialization, etc., however, this does not apply to 4.X, since you cannot rely on the viewDidLoad method to be called.

I would like to avoid adding additional flags to detect this in appdelegate, I would prefer to use a reliable way to do this in the UIViewController, but it seems I cannot find anything on the UIViewController life cycle that could help me here.

Any ideas? How do you deal with such situations?

Answer 1

There are no methods in the UIViewController life cycle that will be called when the application moves from the background to the foreground.

If you want this event to trigger a specific block of code, you need to add an observer for the notification named Notification.Name.UIApplicationWillEnterForeground . An example of this might be:

 NotificationCenter.default.addObserver(self, selector: #selector(appMovedToForeground), name: Notification.Name.UIApplicationWillEnterForeground, object: nil) @objc func appMovedToForeground() { //Your code here } 

Keep in mind that you will need to remove the observer to prevent it from running throughout the application.

Answer 2

 - (void)viewWillAppear:(BOOL)animated 

but not

 - (void)viewDidLoad 

Application Delegation Method

- (void)applicationWillEnterForeground:(UIApplication *)applicationUIApplicationDelegate

will be called after the application has come to the fore, although you can add an observer for the UIApplicationWillEnterForegroundNotification in any of your views.