WWDC 2014 Session 205: Creating Extensions for iOS and OS X, Part 1

• Extensions have a separate code signature, entitlements, and container from their parent app.
• They are not a form of app to app IPC and are accessed solely by Apple frameworks (not even Apple’s apps access them directly)

Notification Center Widgets

• Widgets are view controllers — all of the same lifecycle and containment concepts apply.
  • Widget should be ready to display after -viewWillAppear:.
• Notification Center sets the view frame.
  • Height can be set using Autolayout constraints or by setting UIViewController’s preferredContentSize.
  • Content should animate alongside the height change.
    • On iOS, implement -viewWillTransitionToSize:withTransitionCoordinator: and call -animateAlongsideTransition:completion: from the UIViewControllerTransitionCoordinator protocol.
    • On OS X, implement -viewWillTransitionToSize:.
• Implement -widgetPerformUpdateWithCompletionHandler: from the NCWidgetProviding protocol to be notified when to update the widget.
• New “Today Extension” Xcode template on both iOS and OS X for adding a widget target.
• Use UIViewController’s extensionContext (see NSExtensionContext) to call back to the main app from the widget.

Share Extensions

• Set CFBundleName in the extension bundle’s Info.plist to set the display name.
• Set activation rules (ie. the rules that determine when your share extension shows up in the activity picker) by setting a predicate string for the NSExtension -> NSExtensionAttributes -> NSExtensionActivationRule key in Info.plist.
  • Simpler rules can be expressed using one of the condensed rules instead of a predicate.
• Extensions with custom UI can inherit from UIViewController or NSViewController.
• Extensions that want the standard share sheet UI can inherit from SLComposeServiceViewController.
  • Override -presentationAnimationDidFinish to start heavy lifting after presentation is complete.
  • Override -isContentValid to set the enabled status of the Post button.
    • Call -validateContent to manually trigger an update of the Post button status.
  • Set charactersRemaining property to update UI to reflect how many characters are left.
  • Override -didSelectPost to implement upload logic when user taps Post button.
  • Override -configurationItems to provide an array of SLComposeSheetConfigurationItem objects for displaying custom service-specific settings.
• Get data to upload using NSExtensionContext’s inputItems property.
• Must use NSURLSession with a background session configuration (see +[NSURLSessionConfiguration backgroundSessionConfiguration:]) for uploading data.
• Call -[NSExtensionContext completeRequestReturningItems:completionHandler:] after starting the upload to close the share sheet, or -[NSExtensionContext cancelRequestWithError:] if the user cancelled.

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Complete documentation can be found in the App Extension Programming Guide.