Programming in Objective-C, Fifth Edition

Sorting Arrays

If your address book contains a lot of entries, alphabetizing it might be convenient. You can easily do this by adding a sort method to your AddressBook class and by taking advantage of an NSMutableArray method called sortUsingSelector:. This method takes as its argument a selector that the sortUsingSelector: method uses to compare two elements. Arrays can contain any type of objects in them, so the only way to implement a generic sorting method is to have you decide whether elements in the array are in order. To do this, you must add a method to compare two elements in the array.⁴ The result returned from that method is to be of type NSComparisonResult. It should return NSOrderedAscending if you want the sorting method to place ...