Swift app to demonstrate state preservation and restoration APIs.
Created for a presentation at CocoaHeads Dresden on 09 July 2014. The Deckset presentation (rendered as PDF and the Markdown source) is included in the repository. Feel free to contact me for questions: @hagidd.
Last verified with Xcode 10 and iOS 12.0. The app is written in Swift 4.2.
Tags outline the various steps to enable state restoration in iOS apps:
NO_STATE_RESTORATION: The app without state restoration
STATE_RESTORATION_OPT_IN: The app generally enables state restoration, but does not implement it yet
RESTORATION_IDENTIFIERS: The app sets restoration identifiers on view controllers, but the controllers are not restored successfully yet
BASIC_STATE_RESTORATION: Initially created view controllers are restored successfully
RESTORATION_CLASS: Non-initial view controllers are restored, too
STATE_ENCODING: View controllers restore their views' state
SIZE_CLASSES: The window's size classes are preserved
Note: Both to improve the project and to support the current version of Swift, there have been major updates that are not reflected by the tagged commits. The tags are still helpful to follow the various steps, but you should use the latest commit on
master for a working version.
By default, state restoration happens synchronously at launch on the main queue. While you can move work off the main queue, it will still kick in right after app launch and should finish as quickly as possible, which means it cannot easily be adopted by apps that need to log in or fetch a new session on every launch.
Apple also published two very helpful sample projects:
On iOS 13+, it is recommended to (re)store your model-level state using
NSUserActivity. You can get started by reading this blog post.