Random results from NSFetchedResultsController

Question

I have some data in my entity. How can I get all entries in a random order. ie I wanna shuffle all entries again and again.

I found solution of this question here: Shuffling the results from an NSFetchedResultsController. But I would like to get NSFetchedResultsController with results. Any ideas? Maybe using NSPredicate or NSSortDescriptor?

Answer 1

Subclass NSSortDescriptor to change the default sorting behavior. Something like this should work:

@interface RandomSortDescriptor : NSSortDescriptor 
@end

@implementation RandomSortDescriptor

- (id)copyWithZone:(NSZone*)zone
{
    return [[[self class] alloc] initWithKey:[self key] 
                           ascending:[self ascending] selector:[self selector]];
}

- (id)reversedSortDescriptor
{
    return [[[self class] alloc] initWithKey:[self key] 
                           ascending:![self ascending] selector:[self selector]];
}

- (NSComparisonResult)compareObject:(id)object1 toObject:(id)object2 
{
    NSUInteger random = arc4random_uniform(3);
    switch (random)
    {
       case 0:
          return NSOrderedSame
       case 1:
          return NSOrderedDescending;
       case 2:
          return NSOrderedDescending;
     }
}

@end