Best way to persist an array of images? - ios

Question

I'm looking for a way to persist images to an array (or similar) that can be accessed after the app has closed an relaunched -- sorting the images by date is also required. I'm currently able to store the the images to the app's NSDocumentDirectory with the following code:
-(NSString *)currentDateandTime
{
NSDate *today = [NSDate date];
NSDateFormatter *dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setDateFormat:#"MMddyyyy_HHmmss"];
NSString *dateString = [dateFormat stringFromDate:today];
return dateString;
}
-(void)saveImageToDocuments
{
NSData *imageData = UIImagePNGRepresentation(image);
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];
NSString *date = [self currentDateandTime];
NSString *imagePath =[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:#"%#_image.png",date]];
}
This means I've got images where the date/time is in the filenames of the image. What is the best way to go about storing these images in an array or dictionary AND sorting them by date/time. Thanks for reading!

Answer 1

I would save the file names and dates in a plist file which is an array of dictionaries of format: #{ #"filename" : imageFileName, #"date": imageDate }.
When you load that plist into an NSArray, you can easily sort it by date by specifying your own comparison method. e.g:
NSArray *filenames = [[NSArray alloc] initWithContentsOfFile:filePath];
NSArray *sortedFilenames = [filenames sortedArrayUsingComparator:
^NSComparisonResult(NSDictionary *dict1, NSDictionary *dict2)
{
NSDate *date1 = dict1[#"date"];
NSDate *date2 = dict2[#"date"];
return [date1 compare:date2];
}

Answer 2

Store the image data and the dates in some dictionaries, then store those dictionaries in an array, then use NSKeyedArchiver to archive the array.
[NSKeyedArchiver archiveRootObject:imageDictionary toFile:#"imagesArray"];
Then when you want to retrieve it:
NSArray * retrievedImages = [NSKeyedUnarchiver unarchiveObjectWithFile:#"imagesArray"];
Then just compare the dates in the various dictionaries in the retrieved array.