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POobjective-c custom sorting
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copied!<p>So, having struggled with this for too long, without much documentation to go on, I thought I'd share my experience for those few who are even noobier than me. There probably are much cleaner ways of achieving what I did, so please feel free to suggest improvements.</p> <p>Here's what I wanted to do:</p> <p>I have an NSArrayController which manages NSManagedObjects (say Thing). These objects have a name property which is of type NSString. I wanted to sort the array of the array controller using the name of the managed objects. The common way to go about sorting a mutable array of strings should be something like:</p> <pre><code>[myMutableArrayOfStrings sortUsingSelector:@selector(caseInsensitiveCompare:)]; </code></pre> <p>or:</p> <pre><code>NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES selector:@selector(caseInsensitiveCompare:)]; NSArray *descriptorArray = [NSArray arrayWithObject:sortDescriptor]; [myArrayController setSortDescriptors:descriptorArray]; </code></pre> <p>However, if the names happened to be numbers, caseInsensitiveCompare: would sort 11 before 8 (for instance). Also, I wanted a name of a11b to be sorted AFTER a8b, meaning that I needed to chop the names of the managed objects into groups of digits and non-digit characters, then compare those individually.</p> <p>What I came up with, was to make a category of NSString.</p> <p>header file:</p> <pre><code>#import <Foundation/Foundation.h> @interface NSString (MyString) - (NSComparisonResult)myCustomCompare:(NSString *)anotherString; @end </code></pre> <p>implementation file:</p> <pre><code>#import "MyString.h" @implementation NSString (MyString) - (NSComparisonResult)myCustomCompare:(NSString *)anotherString { elaborate chopping up of strings into substrings.. For each of the 2 strings I made an NSMutableArray. Then I determined if these substrings were NSNumbers, which have their own compare:, or NSStrings (caseInsensitiveCompare:) Then I return an NSComparisonResult (NSOrderedAscending, NSOrderedSame or NSOrderedDescending) } @end </code></pre> <p>Then, in the implementation file of my Thing ManagedObject, I overrid the </p> <pre><code>- (NSComparisonResult)compare:(Thing *)anotherThing { return [self.name myCustomCompare:anotherThing.name]; } </code></pre> <p>One also needs to import MyString.h in the Thing class.</p> <p>Now, using </p> <pre><code>[[myArrayController arrangedObjects] sortUsingSelector:@selector(compare:)]; </code></pre> <p>works like a charm.</p> <p>Just one thing that's been bugging me. If a Thing's name property would contain decimal numbers, like for instance a1.4b and a1.39b, how would I be able to isolate these from the name? (a1.4b would incorrectly be sorted before a1.39b) To make things even worse, a user could enter a Thing's name to be 1.3.55 ...</p>

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