Overview
This lecture covers the UIApplicationDelegate protocol in UIKit, which manages shared behaviors and app life-cycle events in iOS apps.
UIApplicationDelegate Overview
- UIApplicationDelegate is a protocol that defines methods for managing app-level behavior.
- The app delegate object acts as the root of your app and coordinates with the UIApplication object.
- UIKit creates the app delegate early in the app launch cycle and it is always present.
Main Responsibilities of the App Delegate
- Initializes central data structures when the app launches.
- Configures app scenes for multi-window support.
- Responds to external notifications, such as memory warnings and download completions.
- Handles app-level events that are not specific to views or controllers.
- Registers required services like Apple Push Notification service at launch.
Handling App Life Cycle
- Manages events such as app launch, foreground entry, background entry, and termination.
application(_:willFinishLaunchingWithOptions:) is called at the start of launch.application(_:didFinishLaunchingWithOptions:) is called when launch is nearly complete.- Methods exist to handle entering background, becoming active, receiving memory warnings, etc.
- Deprecated methods exist for older iOS versions.
Scene Management
application(_:configurationForConnecting:options:) provides configuration for new scenes.application(_:didDiscardSceneSessions:) informs when scenes are closed by the user.
State Restoration
- Methods allow saving and restoring the app's UI and data state securely.
- State restoration uses version and timestamp metadata for accurate restoration.
Background Execution and Notifications
- Handles background data downloads and responds to remote notifications.
- Manages registration for remote notifications and processes notification-related events.
Other Delegated Events
- Responds to changes in protected data availability.
- Opens URLs and manages app extension permissions.
- Handles WatchKit, HealthKit, SiriKit, and CloudKit events.
Key Terms & Definitions
- UIApplicationDelegate — Protocol for managing app-level behaviors.
- App Delegate — The object that adopts UIApplicationDelegate and manages shared app events.
- Scene — An instance of the app's UI for multitasking.
- State Restoration — The process of saving and restoring app UI and data state.
- Remote Notification — Messages sent to the app from a remote server via APNs.
Action Items / Next Steps
- Review specific delegate method signatures for implementation.
- Study life cycle event handling for both single and multi-scene apps.
- Understand deprecated methods and their modern replacements.