Sorting NSOrderedSet using NSSortDescriptor

Question

When executing this code:

NSSortDescriptor *sortDescriptor = [Characteristic sortDescriptor];
[workingSet sortUsingComparator:[sortDescriptor comparator]];

I get this error:

*** -[NSMutableOrderedSet sortUsingComparator:]: comparator cannot be nil

sortDescriptor is non-nil, so I've no idea why this doesn't work.

I can work around the problem with the code below, which works perfectly:

NSSortDescriptor *sortDescriptor = [Characteristic sortDescriptor];
NSArray *workingArray = [[workingSet array] sortedArrayUsingDescriptors:[NSArray arrayWithObject:sortDescriptor]];
workingSet = [NSMutableOrderedSet orderedSetWithArray:workingArray];

Answer 1

Check out the NSArray reference for the difference between the two methods

A typical usage for the first method would be something like this

NSArray *sortedArray = [array sortedArrayUsingComparator: ^(id obj1, id obj2) {

    if ([obj1 integerValue] > [obj2 integerValue]) {
        return (NSComparisonResult)NSOrderedDescending;
    }

    if ([obj1 integerValue] < [obj2 integerValue]) {
        return (NSComparisonResult)NSOrderedAscending;
    }
    return (NSComparisonResult)NSOrderedSame;
}];

(Example from Apple)

Where as the second method would be more like:

NSSortDescriptor *nameSort = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
NSArray *sortDescriptors = [NSArray arrayWithObject:nameSort];

NSArray *sortedArray = [array sortedArrayUsingDescriptors:sortDescriptors];