http://iosdevlog.com/wwdc/2015/11/16/195196-wwdc2015-226-advanced-nsoperations/
Summary
Operations abstract logic
Dependencies clarify intent
Describe complex behaviors
Enables powerful patterns
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
