applicationDidEnterBackground

applicationDid... refers to a set of lifecycle methods in the iOS UIApplicationDelegate protocol whose names begin with the prefix applicationDid. These methods allow an app to respond to changes in its execution state, such as launching, becoming active, or entering the background. They are called by the system at key moments in the app’s life cycle and are commonly implemented to initialize resources, save state, and manage tasks that should pause or resume with the app’s state.

Common examples include: application:didFinishLaunchingWithOptions:, called after the app has launched and initialized; used for setup and configuration, usually returning true to indicate successful launch. applicationDidBecomeActive:, called when the app transitions from an inactive to an active state; used to resume tasks and refresh UI as needed. applicationWillResignActive:, called when the app is about to move from active to inactive; used to pause ongoing tasks and disable timers. applicationDidEnterBackground:, called when the app enters the background; used to release shared resources, save data, and begin background tasks. applicationWillEnterForeground:, called as the app moves from the background to the foreground; used to undo changes made on entering the background. applicationWillTerminate:, called when the app is about to terminate; used for final data saving and cleanup; note that it is not guaranteed to be called in all termination scenarios.

Since iOS 13, many apps use scenes (SceneDelegate) to manage per‑scene lifecycles, while the app delegate handles global events. For scene-based apps, similar per-scene methods exist (for example, sceneWillEnterForeground and sceneDidBecomeActive), complementing the applicationDid... methods. Implement only the methods you need and keep work in didFinishLaunchingWithOptions lightweight.