Detect when the View has been (re)shown

Question

As the title suggests, how can I detect when a user sees a UIViewController. This is slightly different from viewDidLoad() and viewDidAppear(), both of which are run only when the app is first launched. What I am looking for is something like viewDidAppear(), but runs every time the view literally appears to the user (i.e. when the app is re-opened from the background or when the app is shown after the device is re-woken from sleep).

Thanks!

Possible duplicate of [UIView did appear?](https://stackoverflow.com/questions/5060958/uiview-did-appear) — Paul Peelen, Dec 05 '18 at 15:24
viewDidAppear call every time you show your view controller, viewDidLoad called once when VC created — canister_exister, Dec 05 '18 at 15:25
Create a variable in user defaults and increase it in `viewDidAppear()` — ielyamani, Dec 05 '18 at 15:35

score 1 · Accepted Answer · answered Dec 05 '18 at 15:26

viewDidAppear actually happens every time that view "appears", rather than just once on app load. For example, in an application that uses a UITabBarController, every time you press a tab, the view will switch to a specific view controller and the view controller's viewDidAppear method will get called.

To detect when the view appears from the background you need to register for notifications for applicationDidBecomeActive.

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

The notification is exactly what I was looking for. Thanks! – Microbob Dec 05 '18 at 15:39 — Microbob, Dec 05 '18 at 15:39

Detect when the View has been (re)shown

1 Answers1