iOS Persistence Techniques

• NSUserDefaults
• Documents Directory
• NSCoder
• Core Data

To really grasp this one needs to understand the app lifecyle in iOS. But, first let’s introduce the AppDelegate

application(_:willFinishLaunchingWithOptions:) and application(_:didFinishLaunchingWithOptions:) are invoked right before the app launches, but are only invoked once for each time the app transitions from not running to active.

applicationDidBecomeActive(_:) is called every time the app becomes active from any state, and may be called multiple times.