Question

This has been bugging me for 2 days now and I cant get my head around it. I want to extract several images that are stored in my core data store. The images are user selected using the image picker and rendered to a size of less then 70KB, transformed to data and popped into the core data store. The images are to be used in a slideshow. Entity is called ImageCD and the image is stored in the attribute friendsPhoto. I also allocate a date attribute to sort the images. This is done when the image is saved and is also an attribute of ImageCD.

I am using the following code to TRY and set the array but it does not return anything. im not getting a (NULL) readout on the debugger just that “Number of elements in array = 0;”

NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:&sortDescriptor count:1];
NSLog(@"array's content sortDe:%@",sortDescriptors);

NSMutableArray* sortedImages = [[NSMutableArray alloc] initWithObjects:imageCD.friendsPhoto, nil];
[sortedImages sortUsingDescriptors:sortDescriptors];
[sortDescriptor release];
[sortDescriptors release]; 
NSLog(@"array's content:%@",sortedImages);


imageArray = [[NSMutableArray alloc]init] ;
self.imageArray = sortedImages;
NSLog (@"Number of elements in array = %i", [imageArray count]);


self.theImageView.animationImages = [[NSArray alloc] initWithArray:imageArray];
NSLog(@"animationImages:%@",self.theImageView.animationImages);

So, what am I doing wrong? I have my suspicions it is something to do with this line of code…

NSMutableArray* sortedImages = [[NSMutableArray alloc] initWithObjects:imageCD.friendsPhoto, nil];

But cant work out what the alternate should be. I will be forever indebted to whoever can correct my mistake. I thank you in advance and please, let me know if you require any further information, a beer or a bacon sandwich.

Ohh, to save my sanity, I sanity checked the images by adding a class from my previous app (My Outfit) which utilizes this approach to retrieving images from core data BUT within a tableView, so called in cellForRowInIndexPath etc. and all the images are sound.

DetartrateD

 2011-08-04 19:40:33.051 My Class Book[1027:707] After managedObjectContext:         <NSManagedObjectContext: 0x1821b0>
2011-08-04 19:40:33.057 My Class Book[1027:707] array's content sortDe:(
"(date, ascending, compare:)"
   )
  2011-08-04 19:40:33.059 My Class Book[1027:707] array's content:(
)
2011-08-04 19:40:33.061 My Class Book[1027:707] Number of elements in array = 0
2011-08-04 19:40:33.063 My Class Book[1027:707] animationImages:(
)

Now fixed with these changes
…

NSMutableArray *mutableFetchResultsA = [[managedObjectContext  executeFetchRequest:requestA error:&error] mutableCopy];
if (mutableFetchResultsA == nil) {
    NSLog(@"Testing: No results found");

}
else {

    NSLog(@"Testing: %d Results found.", [mutableFetchResultsA count]);
    NSLog(@"array's content sortDe:%@",mutableFetchResultsA);
}   
[sortDescriptor release];
[sortDescriptors release]; 


imageArray = [[NSMutableArray alloc]init] ;
self.imageArray = [mutableFetchResultsA valueForKey:@"friendsPhoto"];

[mutableFetchResultsA release];
[requestA release];

…

Answer 1

Assuming that the images are stored as NSData * attributes in the ImageCD entity, here is what you need to do:

self.imageArray = [self getImagesInManagedObjectContext:self.managedObjectContext];

Here is the getImagesInManagedObjectContext: method. This method retrieves from the Core Data store the ImageCD objects, sorted using your attribute as required, then creates and returns an autoreleased NSMutableArray of UIImage * objects or nil if no objects have been found.

- (NSMutableArray *) getImagesInManagedObjectContext:(NSManagedObjectContext *)moc{
    NSFetchRequest *request = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"ImageCD" inManagedObjectContext:moc];
    [request setEntity:entity];

    // Edit the sort key as appropriate.
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"date" ascending:YES];
    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:sortDescriptor, nil];
    [request setSortDescriptors:sortDescriptors];

    NSError *error = nil;
    NSMutableArray *array = [NSMutableArray arrayWithArray: [moc executeFetchRequest:request error:&error]];
    [request release];
    [sortDescriptor release];
    [sortDescriptors release];
    if (array && [array count] && !error){
                // create an array of images
                NSMutableArray *images = [[NSMutableArray alloc] init];
                for(ImageCD *obj in array){
                   UIImage *img = [UIImage imageWithData: (NSData *) obj.friendsPhoto];
                   [images addObject:img];
                }

        return [images autorelease];
    }
    else
        return nil;

}