Tag: IOS app lifecycle

iOS – How To Manage App’s Life Cycle In iOS ?

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In this article, We will understand how to manage App’s Life Cycle in iOS. We will discuss how to respond to system notifications when our app is in the foreground or background, and handle other significant system-related events.

For Understanding the App’s Lifecycle concepts, We will discuss on the below topics:

  • Overview
  • Respond to The Scene-Based Life-Cycle Events
  • Responds to App-Based Life-Cycle Events
  • Respond to Other Significant Events

A famous quote about Learning is :

” One learns from books and example only that certain things can be done. Actual learning requires that you do those things. “

So Let’s begin.


Overview

The current state of our app determines what it can and cannot do at any time. For example, a foreground app has the user’s attention, so it has priority over system resources, including the CPU. By contrast, a background app must do as little work as possible, and preferably nothing, because it is offscreen. As our app changes from state to state, we must adjust its behavior accordingly.

When our app’s state changes, UIKit notifies us by calling methods of the appropriate delegate object:

  • In iOS 13 and later, use UISceneDelegate objects to respond to life-cycle events in a scene-based app.
  • In iOS 12 and earlier, use the UIApplicationDelegate object to respond to life-cycle events.

If we enable scene support in our app, iOS always uses our scene delegates in iOS 13 and later. In iOS 12 and earlier, the system uses our app delegate.


Respond to The Scene-Based Life-Cycle Events

If our app supports scenes, UIKit delivers separate life-cycle events for each. A scene represents one instance of our app’s UI running on a device. The user can create multiple scenes for each app, and show and hide them separately. Because each scene has its own life cycle, each can be in a different state of execution. For example, one scene might be in the foreground while others are in the background or are suspended.

Scene support is an opt-in feature. To enable basic support, add the UIApplicationSceneManifest key to our app’s Info.plist file.

The following figure shows the state transitions for scenes. When the user or system requests a new scene for our app, UIKit creates it and puts it in the unattached state. User-requested scenes move quickly to the foreground, where they appear onscreen. A system-requested scene typically moves to the background so that it can process an event. For example, the system might launch the scene in the background to process a location event. When the user dismisses our app’s UI, UIKit moves the associated scene to the background state and eventually to the suspended state. UIKit can disconnect a background or suspended scene at any time to reclaim its resources, returning that scene to the unattached state.

We use scene transitions to perform the following tasks:

  • When UIKit connects a scene to our app, configure our scene’s initial UI and load the data our scene needs.
  • When transitioning to the foreground-active state, configure our UI and prepare to interact with the user.
  • Upon leaving the foreground-active state, save data and quiet our app’s behavior.
  • Upon entering the background state, finish crucial tasks, free up as much memory as possible, and prepare for our app snapshot.
  • At scene disconnection, clean up any shared resources associated with the scene.
  • In addition to scene-related events, we must also respond to the launch of our app using our UIApplicationDelegate object.


Responds to App-Based Life-Cycle Events

In iOS 12 and earlier, and in apps that don’t support scenes, UIKit delivers all life-cycle events to the UIApplicationDelegate object. The app delegate manages all of your app’s windows, including those displayed on separate screens. As a result, app state transitions affect our app’s entire UI, including content on external displays.

App State Transitions

The following figure shows the state transitions involving the app delegate object. After launch, the system puts the app in the inactive or background state, depending on whether the UI is about to appear onscreen. When launching to the foreground, the system transitions the app to the active state automatically. After that, the state fluctuates between active and background until the app terminates.

We use app transitions to perform the following tasks:

  • At launch, initialize our app’s data structures and UI.
  • At activation, finish configuring our UI and prepare to interact with the user.
  • Upon deactivation, save data and quiet our app’s behavior.
  • Upon entering the background state, finish crucial tasks, free up as much memory as possible, and prepare for our app snapshot.
  • At termination, stop all work immediately and release any shared resources.


Respond to Other Significant Events

In addition to handling life-cycle events, apps must also be prepared to handle the events listed in the following below points. We can use our UIApplicationDelegate object to handle most of these events. In some cases, we may also be able to handle them using notifications, allowing us to respond from other parts of our app.

  • Memory warnings – Received when our app’s memory usage is too high. Reduce the amount of memory our app uses.
  • Protected data becomes available/unavailable – Received when the user locks or unlocks their device. We use applicationProtectedDataDidBecomeAvailable(_:) and applicationProtectedDataWillBecomeUnavailable(_:) methods to check protected data availability.
  • Handoff tasks – Received when an NSUserActivity object needs to be processed. We can use application(_:didUpdate:) method to handoff tasks.
  • Time changes – Received for several different time changes, such as when the phone carrier sends a time update. We can use applicationSignificantTimeChange(_:) method to see time changes.
  • Open URLs – Received when your app needs to open a resource. We can use application(_:open:options:) method to open URLs.

That’s all about in this article.


Conclusion

In this article, We understood how to manage App’s Life Cycle in iOS. We also discussed how to respond to system notifications when our app is in the foreground or background, and handle other significant system-related events in iOS.

Thanks for reading ! I hope you enjoyed and learned about App’s Lifecycle Management Concepts in iOS. Reading is one thing, but the only way to master it is to do it yourself.

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