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State transfer from iPhone to Apple Watch
Artemiy Sobolev Software Developer, Parallels Inc.
Agenda
• Parallels Access for Apple Watch
• Architecture design goals
• Living objects tree
• How can it be better with watchOS 2
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Parallels Access
• Simple yet powerful remote client with great usability
3
Parallels Access for Apple Watch:
Usability scenarios
• Checkout computers’ availability
• Connect/Disconnect
• Media control
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iOS 8 and watchOS 1
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iOS 8 and watchOS 1
Parent applicationWatchKit extension
App Store
WatchKit app
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iOS 8 and watchOS 1
Parent applicationWatchKit extension
App Store
WatchKit app
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iOS 8 and watchOS 1
Parent application
WatchKit extension
App Store
WatchKit app
Parent application
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Architecture design goals
• Reduce dependency for core components
• Delta updates
• Transfer changes from iPhone to Watch at any time
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Live objects tree abstraction
Process A,
Machine aProcess B,
Machine b
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Process A,
Machine aProcess B,
Machine b
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine b
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine b
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine b
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine bProcess C,
Machine c
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine bProcess C,
Machine c
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine bProcess C,
Machine c
Live objects tree abstraction
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Process A,
Machine aProcess B,
Machine bProcess C,
Machine c
Live objects tree abstraction
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Parallels Access application
Parallels Access extension
Live objects tree abstraction
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Parallels Access application
Watch app architecture
•No delegates
•No notifications
•KVO only
•Special ViewModels
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How we achieve this sync mechanism
• Reliable iCloud sync mechanism:
• NSFileCoordinator
• NSFilePresenter
• File wrappers
• NSCoding
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Turning on App Groups capability
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NSFileCoordinator + NSFilePresenter
«Don’t implement NSFilePresenter on your own»
- Dave Delong on StackOverflow
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NSFileCoordinator
• Initialized for each file operation
• Coordinates file reading and writing
• Not async
• Contains list of coordination methods
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NSFilePresenter Protocol
• Required properties:
presentedItemURL: NSURL
presentedItemOperationQueue: NSOperationQueue
• To add/remove file presenter call:
NSFileCoordinator.addFilePresenter(…)
NSFileCoordinator.removeFilePresenter(…)
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NSFilePresenter callbacks
• presentedItemDidChange
• presentedItemDidMoveToURL:
• presentedItemDidGainVersion:
• presentedItemDidLoseVersion:
• presentedItemDidResolveConflictVersion:
• NSFileVersion
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File Wrappers
Xcode.app
ContentsMacOSXcode
• Directory with extension
• Helps isolate content
• All apps and frameworks are file wrappers
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File Wrappers + File Presenter
<host id>.paxhost
hostInfo.plist
img.png
• File Presenter can present directory
• The same callbacks:
presentedItem -> presentedSubitem
• All callbacks in one place
• Diminishes the need to merge changes
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Things to consider
• Requires minimum 3 queues
• System holds strong references to file presenters
• Memory limit for extension is ~10 MB
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watchOS 2
Watch Connectivity
Parent Application
extension
• WCSession with the Delegate
• File Transfer
• Application context
• Interactive Messaging
• User info
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Other uses of approach
• The same mechanism with WCSession’s file transfer
• Sync state between
• iOS devices and Macs via iCloud
• iOS application and extension
• 2 iOS applications
• 2 different Mac applications
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State transfer from iPhone to Apple Watch
Artemiy Sobolev
Software Developer, Parallels Inc. c
32
