Implements the boilerplate required to update a UITableView based on results from an NSFetchedResultsController

FetchResultsTableViewUpdater.h

#import <Foundation/Foundation.h>
#import <UIKit/UIKit.h>

@import CoreData;

typedef NS_ENUM(NSUInteger, FetchResultControllerMode) {
    FetchResultsTableViewUpdaterModeMultipleSection,
    FetchResultsTableViewUpdaterModeSingleFixedSection
};

/**
* Implements the boilerplate required to update a UITableView based on results from an NSFetchedResultsController
*
* Can be used to control all sections in a UITableView
* - use mode == FetchResultControllerModeMultipleSection
* - fixedSectionIndex is then ignored.
*
* OR multiple instances of NSFetchedResultsController can be used to each control a single section.
*
* - use mode == FetchResultControllerModeSingleFixedSection
* - fixedSectionIndex is the index of the section this NSFetchedResultsController is using
*
*/
@interface FetchResultsTableViewUpdater : NSObject <NSFetchedResultsControllerDelegate>
@property(nonatomic, weak) UITableView *tableView;
@property(nonatomic, weak) NSFetchedResultsController *fetchedResultsController;

// Used to pass on calls if required TODO: only used in the didChangeObject call so far
@property(nonatomic, weak) id <NSFetchedResultsControllerDelegate> delegate;

/**
* fixedSectionIndex = only used if mode is FetchResultControllerModeSingleFixedSection, in which case the delegates will always pass fixedSectionIndex for the section.
*/
- (instancetype)initWithTableView:(UITableView *)tableView
         fetchedResultsController:(NSFetchedResultsController *)fetchedResultsController
                             mode:(FetchResultControllerMode)mode
                fixedSectionIndex:(NSInteger)fixedSectionIndex;

@end

FetchResultsTableViewUpdater.m

#import "FetchResultsTableViewUpdater.h"

@interface FetchResultsTableViewUpdater ()
@property(nonatomic) FetchResultControllerMode mode;
@property(nonatomic) NSInteger fixedSectionIndex;
@end

@implementation FetchResultsTableViewUpdater {

}
- (instancetype)initWithTableView:(UITableView *)tableView
         fetchedResultsController:(NSFetchedResultsController *)fetchedResultsController
                             mode:(FetchResultControllerMode)mode
                fixedSectionIndex:(NSInteger)fixedSectionIndex {
    self = [super init];
    if (self) {
        self.tableView = tableView;
        self.fetchedResultsController = fetchedResultsController;
        self.fetchedResultsController.delegate = self;
        self.mode = mode;
        self.fixedSectionIndex = fixedSectionIndex;
    }

    return self;
}

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
    NSLog(@"Beginning updates");
    [self.tableView beginUpdates];
}

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath {

    if (self.mode == FetchResultsTableViewUpdaterModeSingleFixedSection) {
        if (indexPath) {
            indexPath = [NSIndexPath indexPathForRow:indexPath.row inSection:self.fixedSectionIndex];
        }

        if (newIndexPath) {
            newIndexPath = [NSIndexPath indexPathForRow:newIndexPath.row inSection:self.fixedSectionIndex];
        }
    }

    UITableView *tableView = self.tableView;

    switch (type) {

        case NSFetchedResultsChangeInsert: {
            NSLog(@"Inserting at path %@", newIndexPath);
            [tableView insertRowsAtIndexPaths:@[newIndexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            break;
        }
        case NSFetchedResultsChangeDelete: {
            NSLog(@"Deleting at path %ld", (long) indexPath.row);
            [tableView deleteRowsAtIndexPaths:@[indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            break;
        }
        case NSFetchedResultsChangeUpdate:
            NSLog(@"Updating at path %@", indexPath);
            if ([[tableView indexPathsForVisibleRows] containsObject:indexPath]) {
                [tableView reloadRowsAtIndexPaths:@[indexPath]
                                 withRowAnimation:UITableViewRowAnimationFade];
            }
            break;

        case NSFetchedResultsChangeMove:
            NSLog(@"Moving from path %@ to %@", indexPath, newIndexPath);
            [tableView deleteRowsAtIndexPaths:@[indexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:@[newIndexPath]
                             withRowAnimation:UITableViewRowAnimationFade];
            break;
    }

    // Pass on to self.delegate
    if ([((NSObject *) self.delegate) respondsToSelector:@selector(controller:didChangeObject:atIndexPath:forChangeType:newIndexPath:)]) {
        [self.delegate controller:controller
                  didChangeObject:anObject
                      atIndexPath:indexPath
                    forChangeType:type
                     newIndexPath:newIndexPath];
    }
}

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex
     forChangeType:(NSFetchedResultsChangeType)type {
    UITableView *tableView = self.tableView;

    if (self.mode == FetchResultsTableViewUpdaterModeMultipleSection) {
        if (type == NSFetchedResultsChangeInsert) {
            NSLog(@"Inserting section at %lu", (unsigned long) sectionIndex);
            NSIndexSet *insertedSection = [NSIndexSet indexSetWithIndex:sectionIndex];

            [tableView insertSections:insertedSection withRowAnimation:UITableViewRowAnimationFade];
        }
        else if (type == NSFetchedResultsChangeDelete) {
            NSLog(@"Deleting section at %lu", (unsigned long) sectionIndex);
            NSIndexSet *deletedSection = [NSIndexSet indexSetWithIndex:sectionIndex];

            [tableView deleteSections:deletedSection withRowAnimation:UITableViewRowAnimationFade];
        }
    }
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
    NSLog(@"Ending updates");
    NSLog(@"Fetched %ld Items After Change", (unsigned long) self.fetchedResultsController.fetchedObjects.count);
    @try {
        [self.tableView endUpdates];
    }
    @catch (NSException *ex) {
        NSLog(@"RBQFecthResultsTVC caught exception updating table view: %@. Falling back to reload.", ex);

        // TODO: no 'reset' method on real NSFetchedResults controller
//        [self.fetchedResultsController reset];

        [self.tableView reloadData];
    }
}

@end