摘要： Selectors identify the messages that are sent to Objective-C objects.They’re used bythe receivers of messages to select which methods will be performed.In particular, selectors are key to Cocoa’simplementation of the Notifications, Delegates,Targets and Actions, Invocations, and Forwardingpatterns. 阅读全文

摘要： Enumerators provide a mechanism for accessing all of the objects in a collection sequentiallywithout exposing the collection’s underlying data structures. Enumerators areused to write flexible and efficient code for using collection classes without tying applicationsto specific implementations. Furt 阅读全文