WWDC App

  • Download Settings
  • Download Schedule
  • Download News
  • Download Video list
  • Mark Favorites
  • Leave Feedback
  • Log In
  • Developer Status
  • Download Pass
  • Download Photos
  • Watch Videos
  • Push Notifications
  • Access CloudKit
  • Location Permission
  • Display Alerts Upload
  • Analytics

Agenda

  • Core Concepts
  • Beyond the Basics
  • Sample Code

Core Concepts

  • High-level dispatch_queue_t
  • Cancellation
  • maxConcurrentOperationCount

Serial Queues

maxConcurrentOperationCount = 1

Concurrent Queues

maxConcurrentOperationCount = Default

NSOperation

  • High-level dispatch_block_t
  • Long-running task
  • Subclassable

Lifecycle of an NSOperation

1

Cancellation

var cancelled: Bool { get }
  • Only changes state
  • Subclasses dictate meaning
  • Susceptible to race conditions
operationA.cancel()

Readiness

var ready: Bool { get }

Execute when ready

Serial Operation Queues

  • Readiness

Dependencies

  • “First this, then that”
  • Strict ordering
  • Implemented via readiness
  • Not limited by queues
let operationA = ...
let operationB = ...
operationB.addDependency(operationA)
  • Operation deadlock

WWDC App Favorites

2

WWDC App Startup

3

Abstraction

  • Operations abstract logic
  • Simplifies logic changes
  • WWDC app
    • Custom backend CloudKit
  • Grand Central Dispatch?

Beyond the Basics

UI Operations

Not just the background

  • Authentication Videos
  • Alerts
  • “Modal” UI

Block Operations

4

It’s blocks all the way down

  • NSOperation to execute a block
  • Dependencies for blocks
  • Leaving feedback

WWDC App

  • Block operations

Generating Dependencies

When two operations love each other…

  • “Never execute this until after executing that”
  • Saving a favorite
  • Downloading pass
  • Anything requiring login

WWDC app favorites

5

Extending Readiness

Adding requirements

  • “Only execute this if…”

  • Examples

    • Network is reachable
    • Access to user location
    • User is “logged in”

Composing Operations

Downloading and parsing

6

I heard you like operations…

  • Downloading and parsing
  • Fetching favorites

WWDC App

Fetching favorites

override public func execute() {
	let userRecordID: CKRecordID = ...
	let predicate = NSPredicate(format: "creatorUserRecordID = %@", userRecordID)
	let query = CKQuery(recordType: "SessionFavorite", predicate: predicate)
	let queryOperation = CKQueryOperation(query)
	executeQueryOperation(queryOperation)
}

private func executeQueryOperation(queryOperation: CKQueryOperation) {
	queryOperation.recordFetchedBlock = ...
	queryOperation.queryCompletionBlock = { cursor, error in
		if let error = error {
			self.finishWithError(error)
		} else if let cursor = cursor {
			let fetchMoreRecords = CKQueryOperation(cursor)
				self.executeQueryOperation(fetchMoreRecords)
		} else {
			self.processFetchedRecords()
		}
	}
	database.addOperation(queryOperation)
}

Mutual Exclusivity

There can be only one

  • Alerts
  • Videos
  • Loading database

One alert at a time

7

Sample Code

  • Earthquakes and Operations <developer.apple.com/wwdc>

Operation

  • NSOperation subclass
  • Adds “conditions”
  • Adds “observers”

  • Example operations

    • Groups
    • URLSessionTask
    • Location
    • Delay

OperationCondition

  • Generates dependencies
  • Defines mutual exclusivity
  • Checks for satisfied conditions
  • Example conditions
    • MutuallyExclusive
    • Reachability
    • Permissions

OperationObserver

  • Notified about significant events
    • Operation start
    • Operation end
    • Operation generation
  • Example observers
    • Timeouts
    • Background tasks
    • Network activity indicator

Summary

  • Operations abstract logic
  • Dependencies clarify intent
  • Describe complex behaviors
  • Enables powerful patterns
  • Building Responsive and Efficient Apps with GCD CloudKit Tips and Tricks
  • Advanced CloudKit
  • Nob Hill Pacific Heights （WWDC14）