How to know when View will become active from background

applicationdidenterbackground objective-c
uiapplicationdidbecomeactivenotification swift 4
applicationdidenterbackground swift
willenterforegroundnotification
didenterbackgroundnotification
swift check if app is in background
willresignactivenotification
uiapplicationwillresignactivenotification

Is there no method similar to the applicationDidBecomeActive, but that applies to a view controller. I know about viewWillAppear, and viewDidAppear, which work when you navigate to this view controller, but I need something that is called when the user leaves the app (by pressing home button) and then re-opens the app. I have a global variable that is defined in the viewDidLoad of the view controller, but is redefined in the applicationDidBecomeActive method. This means that if the app enters background, and then comes back to the foreground the variable will change. And I need to reset it in something like a viewDidBecomeActive method.


You can simply register your view controller to listen to UIApplicationDidBecomeActiveNotification notification.

Add the following in your view controller's viewWillAppear method:

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

ViewDidAppear is not called when opening app from background , 2013-04-07 09:31:06.505 myapp[15459:11303] view did load 2013-04-07 app did become active 2013-04-07 09:31:06.512 myapp[15459:11303] did won't be called when app comes back from background to foreground. use this method to tell the child that its views are about to appear or disappear. You don't necessarily need to pause the timer, though. If you don't do anything, the app will get put to sleep anyway and won't execute any code. Presumably your timer will fire when you become active again (if you do). If you need to do something special there are 'did become active' delegate methods and notifications you can register for as well.


Swift 4

NotificationCenter.default.addObserver(
    self,
    selector:#selector(refreshWhenAppBecomesActive),
    name: NSNotification.Name.UIApplicationDidBecomeActive,
    object: nil)

What's The Difference Between viewWillAppear or viewDidLoad , For example, if a user is registering for an account, they should see a screen When they are done, they can be taken to a screen that shows them their state of the application, indicating that the view controller is becoming “active. Sometimes, you need to modify an image before you set it as the background of a button. Doing good background research on a doctor is a good way to gain confidence in your choice before you ever see that doctor. When coupled with general advice about choosing the right doctor for you, you have a far better chance of being satisfied with the relationship.


Swift 5

    NotificationCenter.default.addObserver(
        self,
        selector:#selector(yourMethod),
        name: UIApplication.didBecomeActiveNotification,
        object: nil)

and at your function

@objc func yourMethod() {
   // your code
}

How to detect when app moves to background or foreground, If you want to know how your app is going to the background, or it's this notification, you can be aware when your app moves to background:. Check out the following ways on how to view these hidden programs: Using Task Manager #1: Press "Ctrl + Alt + Delete" and then choose "Task Manager". Alternatively you can press "Ctrl + Shift + Esc" to directly open task manager. #2: To see a list of processes that are running on your computer, click "processes".


iOS View Controller Life Cycle - Good Morning Swift, What you will learn from this tutorial : View controller can override this method to make changes before the view lays out its subviews. Be aware that if the memory of your app goes over a certain threshold, iOS will shutdown your app. Click or tap the Task View button. The screen clears, and Windows displays miniature views of your open apps and programs, shown here. Click the Task View button to see thumbnail views of each of your currently running apps and programs. Tap or click any thumbnail to return the app or program to full size.


applicationWillEnterForeground(_:), In iOS 4.0 and later, this method is called as part of the transition from the background to the active state. You can use this method to undo many of the changes  Learn how to add an active class to the current element with JavaScript. If you do not have an active class set on the button element to start with, use the following code:


applicationWillResignActive(_:), An app in the inactive state should do minimal work while it waits to transition to either the active or background state. If your app has unsaved user data, you can​  or Public Authority to be an IHSS provider, as long as you are an active provider and your criminal background check remains clear, you will continue to be eligible to provide services for any IHSS recipient. If you have any questions about these provider enrollment requirements, contact your County IHSS Office or IHSS Public Authority.