Performance issues using NSFetchedResultsController with sectionNameKeyPath - ios

Question

I have a huge amount of data inside CoreData (around 10.000 objects).
I want to show them in sections, therefore I'm using:
+ (NSFetchedResultsController*) eventsFetchResultControllerWithSearchString:(NSString*) searchString andFilter:(EventFilters) filter
{
NSSortDescriptor *sort = [[NSSortDescriptor alloc] initWithKey:#"ts" ascending:NO];
NSArray* sortDescriptors = #[sort];
NSPredicate* filterPredicate = [NSFetchedResultsController eventsPredicatesWithSearchString:searchString andFilter:filter];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *callEntity = [NSEntityDescription entityForName:#"EventDB" inManagedObjectContext:[[AppManager sharedAppManager] managedObjectContext]];
[fetchRequest setEntity:callEntity];
[fetchRequest setPredicate:filterPredicate];
[fetchRequest setFetchBatchSize:20];
[fetchRequest setSortDescriptors:sortDescriptors];
NSString* sectionKeyPath = #"timestamp.relativeDate";
if(searchString)
{
sectionKeyPath = nil;
}
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:[[AppManager sharedAppManager] managedObjectContext]
sectionNameKeyPath:sectionKeyPath
cacheName:nil];
NSError *error = nil;
if (![aFetchedResultsController performFetch:&error])
{
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
return aFetchedResultsController;
}
On my UITableView I have:
- (CGFloat) tableView:(UITableView *)tableView heightForRowAtIndexPath:(NSIndexPath *)indexPath
{
CGFloat emptyCellHeight = [super tableView:tableView noDataCellHieghtAtIndexPath:indexPath forCellType:kUITableViewCellTypeNoDataCell];
if(emptyCellHeight != 0.0f)
{
return emptyCellHeight;
}
if(self.measurementCell == nil)
{
NSArray *topLevelObjects = [[NSBundle mainBundle] loadNibNamed:#"EventCell" owner:self options:nil];
self.measurementCell = [topLevelObjects objectAtIndex:0];
}
EventDB *event = [[self fetchedResultsControllerForTableView:tableView] objectAtIndexPath:indexPath];
return [self.measurementCell calculateHeightForEvent:event];
}
- (CGFloat) tableView:(UITableView *)tableView estimatedHeightForRowAtIndexPath:(NSIndexPath *)indexPath
{
return 100.0f;
}
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView
{
if(self.tableView == tableView && [[self fetchedResultsControllerForTableView:tableView].sections count] == 0)
{
return 1;
}
return [[[self fetchedResultsControllerForTableView:tableView] sections] count];
}
- (NSString *)tableView:(UITableView *)tableView titleForHeaderInSection:(NSInteger)section
{
NSArray* sections = [[self fetchedResultsControllerForTableView:tableView] sections];
if(section < [sections count])
{
id <NSFetchedResultsSectionInfo> theSection = [sections objectAtIndex:section];
return [theSection name];
}
return nil;
}
I found a solution to improve height calculations using estimatedHeight, but when I turned on sectionNameKeyPath it got really slow.
I suspect it is because it loads all elements to read all sections at start.
Is there any way to optimize that part ? Something like estimatedHeight but for sections ?