NSArray class 的“sortedArrayHint”方法，这个方法的目的是什么，它是如何使用的？

Question

Question is the same as the title. ("sortedArrayHint" method of NSArray class, what is the purpose of this method and how is it used)

I read documentation but the explanation is not clear.

Please explain the purpose of this method and its usage.

Answer 1

The idea is simple. Assume you have a large array that should always be sorted. Changing or inserting even one element means you have to resort the array. Sorting is costly.

The method -[NSArray sortedArrayHint] can be called on an already sorted array in order to get private internal data that can be used to speed up a sort of the same array given that only a small change has been made.

Usage is simple:

1. Get and store the hint from the original sorted array using -[NSArray sortedArrayHint] .
2. After a small change; resort using -[NSArray sortedArrayUsingFunction:context:hint:] with the stored hint.
3. After a large change; resort using -[NSArray sortedArrayUsingFunction:context:] , and get a new hint.

What is a small, or large, change is something you must measure with Instruments.

I never use this myself, since I have found it more effective to use my own categories on NSArray and NSMutabelArray for sorted inserts, that uses a binary search, on sorted array. My code is available as open source here: https://github.com/Jayway/CWFoundation