Efficient way to obtain section index from NSFetchedResultsController grouped by date - ios

Question

I am building a calendar for iOS based on UICollectionView (GitHub link), based on the one that you can find at this repo. The underlying reasoning behind it is well described on this Objc.io issue.
To put it short, the process involves creating a NSFetchedResultsController that queries the events grouping them by day and displaying them in a (customized) UICollectionView afterwards.
The original calendar has the following inconvenient: since it is based on the sections contained in NSFetchedResultsController, it simply puts the date as the section header but ignores the days where there are no events happening. In this scenario, the index of the section contained in the NSFetchedResultsController matches 1:1 the sections of the calendar.
I made modifications in order to base the calculation of section headers based on calendar days, but now there is not a 1:1 correspondence anymore between the sections in the NSFetchedResultsController and the sections of the UICollectionView. Remember that the sections are based on the days.
This is the way I am currently doing it now, when I need to get the index of the section for a certain day:
- (NSInteger)sectionForDate:(NSDate*)day
{
return [[self.fetchedResultsController.sections valueForKey:#"name"] indexOfObject:[NSString stringWithFormat:#"%#", day]];
}
Here's the question: is there a more efficient way to get the section index out of the NSFetchedResultsController ?
If you think I should have used a different approach, please let me know.

Answer 1

There is absolutely no problem in having different sections from the FRC and in your datasource methods. The logic becomes a little bit more complicated, but it is a not so unusual pattern. There should be no drawbacks in efficiency.
I recently wrote an app where you can even switch between showing all days or only those with events, similar to Apple's calendar where in the list view the "empty" days are skipped as well.