Take the 2-minute tour ×  I was wondering if someone can explain
what is informal protocols in Objective C? I try to understand
it on apple documentation and some other books but my head is
still spinning so i will really appreciate that if someone can
explain with example.   share|improve this question  7 Answers 7
up vote 48 down vote accepted  An informal protocol was, as
Jonnathan said, typically a category declared on NSObject with
no corresponding implementation (most often -- there was the
rare one that did provide dummy implementations on NSObject).
As of 10.6 (and in the iPhone SDK), this pattern is no longer
used. Specifically, what was declared as follows in 10.5 (and
prior):  @interface NSObject(NSApplicationNotifications) -
(void)applicationWillFinishLaunching:(NSNotification
*)notification; @interface NSObject(NSApplicationDelegate) - (NS
ApplicationTerminateReply)applicationShouldTerminate:(NSApplicat
ion *)sender;  Is now declared as:  @protocol
NSApplicationDelegate <NSObject> - (NSApplicatio