applicationDidFinishLaunching

applicationDidFinishLaunching is a term used to describe a callback in Apple platform app lifecycles that signals the completion of an application's launch process. It refers to methods defined in application delegate protocols that give developers a centralized place to perform setup before the app becomes active.

In iOS, the relevant method is application(_:didFinishLaunchingWithOptions:), defined in UIApplicationDelegate. It is called after the app has finished launching and prior to presenting UI to the user. The method returns a Bool indicating whether the app launched successfully. Typical tasks here include configuring services (analytics, logging, dependency injection), restoring state, registering for remote notifications, and performing initial one-time setup. Since the introduction of the scene-based lifecycle in iOS 13, some initialization may occur in scene delegate methods, but the app delegate launch method can still be used for global, non-scene-specific work.

In macOS, the analogous entry point is applicationDidFinishLaunching(_ notification: Notification) in NSApplicationDelegate. This method is invoked once the application has completed its launch sequence and is ready to run the main event loop. It is commonly used to perform startup tasks that affect the entire application, such as setting up menus, initializing shared resources, or preparing state that spans multiple windows.

Best practices for either platform emphasize keeping launch-time work minimal to avoid delaying user interaction, and moving longer or asynchronous tasks off the main thread when appropriate.