Notes WWDC 2019 : Introducing Multiple Windows on iPad

Référence : Session 212 - Introducing Multiple Windows on iPad

Design intent

Where should I add scenes to my app?

The user should be allowed to do everything from just one window (apps cannot require multiple windows).

• Some apps have all features in each window (e.g. Safari, Maps, etc)
• Some apps only have some features in secondary windows “dedicated window” (e.g. Mail compose, etc)

What interactions should create scenes?

Provided by system:

• Plus button in Exposé (top right)
• Drag app icon to the edge of screen

Or provided by the app:

• Master-detail view (drag from master)
• Button

App lifecycle changes

• UIScene
  • Contains UI
  • Created by the system on demand
  • Destroyed by the system when unused
• UISceneSession
  • Persisted interface state
  • Have defined system role
  • Created for new application representations
  • Scenes connect and disconnect from sessions

Migrating your code from:

application(_:didFinishLaunchingWithOptions:)
applicationWillEnterForeground(_:)
applicationDidBecomeActive(_:)
applicationWillResignActive(_:)
applicationDidEnterBackground(_:)
...
application(_:open:options:)
...
application(_:continue:restorationHandler:)

to:

scene(_:willConnectTo:options:)
sceneWillEnterForeground(_:)
sceneDidBecomeActive(_:)
sceneWillResignActive(_:)
sceneDidEnterBackground(_:)
...
scene(_:openURLContexts:)
...
scene(_:continue:)

UIScene state restoration:

• State restoration is now data in the form of NSUserActivity
• Requested from UISceneDelegate
• Accessible at any time via UISceneSession.stateRestorationActivity

Adding support to multiple windows:

• Main target deployment info: check the “support multiple windows” checkbox
• In Info.plist: declare what interfaces for what types of roles
• Edit scene delegate: implement state restoration

Drag and drop

• NSUserActivity based
• Can add to existing NSItemProvider on UIDragItem

Next steps

Difference between “scene” and “window”: a “scene” can be present in the multitasking interface, even if the window is not loaded

Create new scenes:

requestSceneSessionActivation(_:userActivity:options:errorHandler:)

Update existing scenes:

requestSceneSessionRefresh(_:)

Close scenes:

requestSceneSessionDestruction(_:options:errorHandler:)

Examples:

 // Open a new window

@IBAction func handleLongPress(forDocumentAt url: URL) {
  if let existingSession = findSession(for: url) {
    UIApplication.shared.requestSceneSessionActivation(existingSession, userActivity: nil, options: nil)
  } else {
    let activity = NSUserActivity(activityType: "com.example.MyApp.EditDocument")
    activity.userInfo["url"] = url

    UIApplication.shared.requestSceneSessionActivation(nil, userActivity: activity, options: nil)
  }
}

// Close a window

func closeWindow(and action: DraftAction) {
  let options = UIWindowScene.DestructionRequestOptions()

  switch action {
  case .send: options.windowDismissalAnimation = .commit
  case .save: options.windowDismissalAnimation = .decline
  case .delete: options.windowDismissalAnimation = .standard
  }

  let session = view.window!.windowScene!.session
  UIApplication.shared.requestSceneSessionDestruction(session, options: options)
}

For state restoration:

• var stateRestorationUserActivity: NSUserActivity: preferred mechanism
• var persistentIdentifier: String { get }: ID that you can store to manually save/restore the scene state
• var userInfo: [String:AnyHashable]: additional info, for instance data in the NSUserDefaults that are not global to the app (e.g. a panel being displayed)

Debugging tips:

• Every app has unique challenges
• Expect to make changes
• Test, test, and test more
• Focus on multiple scenes
• Review system and custom singletons (UIApplication.shared, etc)