NSNotificationCenter docs: “The method specified by notificationSelector must have one and only one argument”

developer.apple.com/library/ios/documentation/Cocoa/Reference/Foundation/Classes/NSNotificationCenter_Class/index.html#//apple_ref/occ/instm/NSNotificationCenter/addObserver:selector:name:object:

I often see that NSNotificationCenter API violated by using selectors without any arguments.