WWDC Advanced NSOperations
https://developer.apple.com/videos/wwdc/2015/?id=226
WWDC app use NSOperation
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Agenda
Core Concepts
1NSOperationQueue:ahigh-level wrapper around a dispatch queue
1.1 NSOperationQueue makes it easy tocanceloperations that have not yet begun executing
1.2 Serial Queues: set maxConcurrentOperationCount=1 ,load a bundle of operations into this queue,the queue will pull off these operations one by one and execute them in order,the next operation will not begin executing until the previous has finished
1.3 Concurrent Queues:setmaxConcurrentOperationCount=default , run as many as system allows,run multiple operationssimultaneously
2 NSOperation:a high-levelwrapperaround a dispatch block
2.1 it’s class , you can subclass it,provide your own custom logic on how it executes
2.2 lifecycle
2.2.1 cancel
can not change from the “finished” state to the “cancelled” state , If you want cancel an operation ,there are some cases where won’t actually cancel
call cancel method
operationA.cancel()
2.2.2 ready
Serial Queues:which one is ready will execute first , maybe not the the first one pull into the queue
2.3 dependency:express a strict ordering
an operation will become ready if all of its dependencies have finished executing
not limited by queues:If you have two operation queues in your application,operations in the first queue can be dependent on the operations in the second queue
let operationA = ...
let operationB = ...
operationB.addDependency(operationA)
Beyond the Basics
1 UI Operations ,not just the background
Authentication Videos
Alerts
“Modal” UI
2 Block Operations
It’s blocks all the way down
NSOperation to execute a block
Dependencies for blocks
Leaving feedback
3 GeneratingDependencies
When two operations love each other...
“Never execute this until after executing that”
4Mutual Exclusivity
There can be only one
cross-queue dependencies are really powerful
Alerts
Videos
Loading database
Sample Code
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
