Question

I have an NSArray that is extracted from core data. The entities in the array have a date attribute (of type NSDate ofcourse). What I want to do is this:

• The array needs to be displayed in a table view,
• the sections, and their titles are months , of the objects in the array

For example if I have 3 objects (april 1, april 3 & july 7) there should be 2 sections:
– april 2012(2 obj)
– july 2012 (1 obj)).

How do I split the array like this?

Answer 1

Try using a NSFetchedResultsController and a custom sectionNameKeyPath which should be a method in your NSManagedObject subclass.

The fetchedResultsController can be set up as following:

NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"MyObject"];
NSSortDescriptor *sortDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"date" ascending:YES];
request.sortDescriptors = @[sortDescriptor];
NSFetchedResultsController *frc = [[NSFetchedResultsController alloc] initWithFetchRequest:request managedObjectContext:managedObjectContext sectionNameKeyPath:@"monthAsString" cacheName:nil];

You need to implement the monthAsString method in your managedObject subclass. Allocate the NSDateFormatter only once, because it won’t perform well if you allocate a new instance for every call.

 - (NSString *)monthAsString {
    static NSDateFormatter *formatter;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        formatter = [[NSDateFormatter alloc] init];
        formatter.dateFormat = @"MMMM yyyy";
    });

    NSString *dateString = [formatter stringFromDate:self.date];
    return dateString;
 }