What is the lifecycle of an application on iOS?

The application lifecycle on iOS is managed by the system and includes the following states:

1. Not Running: The app is either not launched or has been terminated by the system or user.

2. Inactive: The app is in the foreground but not receiving events (e.g., during an incoming call).

3. Active: The app is in the foreground and actively interacting with the user.

4. Background: The app is in the background. It may perform limited tasks (e.g., data loading, audio playback).

5. Suspended: The app is in the background but not executing code. It remains in memory but can be unloaded by the system when resources are low.

The system informs the app about state changes through methods of the UIApplicationDelegate object.

Examples of methods:

// called before transitioning to Active
func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool

// called when transitioning from Active to Inactive
func applicationWillResignActive(_ application: UIApplication)

// called when transitioning from Inactive to Active
func applicationDidBecomeActive(_ application: UIApplication)

// called when transitioning from Active or Background to Background
func applicationDidEnterBackground(_ application: UIApplication)

// called when transitioning from Background to Foreground (before Active)
func applicationWillEnterForeground(_ application: UIApplication)

// called when the app is about to terminate
func applicationWillTerminate(_ application: UIApplication)