StoreMad/SMCollectionViewDataSource.m

//
//  SMCollectionViewDataSource.m
//  StoreMad
//
//  Created by Andrew Smith on 2/23/13.
//  Copyright (c) 2012 Andrew B. Smith ( http://github.com/drewsmits ). All rights reserved.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
// of the Software, and to permit persons to whom the Software is furnished to do so,
// subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

#import "SMCollectionViewDataSource.h"

@interface SMCollectionViewDataSource ()

@property (nonatomic, strong) NSMutableArray *objectChanges;

@property (nonatomic, strong) NSMutableArray *sectionChanges;

@property (nonatomic, weak) UICollectionView *collectionView;

@end

@implementation SMCollectionViewDataSource

- (id)init
{
    self = [super init];
    if (self) {
        _objectChanges = [NSMutableArray array];
        _sectionChanges = [NSMutableArray array];
    }
    return self;
}

- (void)setupWithCollectionView:(UICollectionView *)collectionView
                   fetchRequest:(NSFetchRequest *)fetchRequest
                        context:(NSManagedObjectContext *)context
             sectionNameKeyPath:(NSString *)sectionNameKeyPath
                      cacheName:(NSString *)cacheName
{    
    // Build controller
    self.fetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
                                                                        managedObjectContext:context
                                                                          sectionNameKeyPath:sectionNameKeyPath
                                                                                   cacheName:cacheName];
    
    // Respond to changes here
    self.fetchedResultsController.delegate = self;
    
    // Hold onto this to work with when changes happen
    self.collectionView = collectionView;
}

#pragma mark - Change

- (void)controller:(NSFetchedResultsController *)controller
  didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex
     forChangeType:(NSFetchedResultsChangeType)type
{
    NSMutableDictionary *change = [NSMutableDictionary new];
    
    switch(type) {
        case NSFetchedResultsChangeInsert:
            change[@(type)] = @(sectionIndex);
            break;
        case NSFetchedResultsChangeDelete:
            change[@(type)] = @(sectionIndex);
            break;
        case NSFetchedResultsChangeUpdate:
            change[@(type)] = @(sectionIndex);
            break;
        case NSFetchedResultsChangeMove:
            // Not handled
            break;
    }
    
    [self.sectionChanges addObject:change];
}

- (void)controller:(NSFetchedResultsController *)controller
   didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath
     forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    NSMutableDictionary *change = [NSMutableDictionary new];
    
    switch(type) {
        case NSFetchedResultsChangeInsert:
            change[@(type)] = newIndexPath;
            break;
        case NSFetchedResultsChangeDelete:
            change[@(type)] = indexPath;
            break;
        case NSFetchedResultsChangeUpdate:
            change[@(type)] = indexPath;
            break;
        case NSFetchedResultsChangeMove:
            change[@(type)] = @[indexPath, newIndexPath];
            break;
    }
    
    [self.objectChanges addObject:change];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{    
    if ([self.sectionChanges count] > 0) {
        [self.collectionView performBatchUpdates:^{
            for (NSDictionary *change in self.sectionChanges) {
                [change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id sectionIndex, BOOL *stop) {
                    NSFetchedResultsChangeType type = [key unsignedIntegerValue];
                    switch (type) {
                        case NSFetchedResultsChangeInsert:
                            [self.collectionView insertSections:[NSIndexSet indexSetWithIndex:[sectionIndex unsignedIntegerValue]]];
                            break;
                        case NSFetchedResultsChangeDelete:
                            [self.collectionView deleteSections:[NSIndexSet indexSetWithIndex:[sectionIndex unsignedIntegerValue]]];
                            break;
                        case NSFetchedResultsChangeUpdate:
                            [self.collectionView reloadSections:[NSIndexSet indexSetWithIndex:[sectionIndex unsignedIntegerValue]]];
                            break;
                        case NSFetchedResultsChangeMove:
                            [self.collectionView moveSection:[sectionIndex[0] unsignedIntegerValue]
                                                   toSection:[sectionIndex[1] unsignedIntegerValue]];
                            break;
                    }
                }];
            }
        } completion:nil];
    }
    
    if ([self.objectChanges count] > 0 && [self.sectionChanges count] == 0) {
        if ([self shouldReloadCollectionViewToPreventKnownIssue]) {
            // This is to prevent a bug in UICollectionView from occurring.
            // The bug presents itself when inserting the first object or deleting the last object in a collection view.
            // http://stackoverflow.com/questions/12611292/uicollectionview-assertion-failure
            // This code should be removed once the bug has been fixed, it is tracked in OpenRadar
            // http://openradar.appspot.com/12954582
            [self.collectionView reloadData];
        } else {
            [self.collectionView performBatchUpdates:^{
                for (NSDictionary *change in _objectChanges) {
                    [change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id indexPath, BOOL *stop) {
                        NSFetchedResultsChangeType type = [key unsignedIntegerValue];
                        switch (type) {
                            case NSFetchedResultsChangeInsert:
                                [self.collectionView insertItemsAtIndexPaths:@[indexPath]];
                                break;
                            case NSFetchedResultsChangeDelete:
                                [self.collectionView deleteItemsAtIndexPaths:@[indexPath]];
                                break;
                            case NSFetchedResultsChangeUpdate:
                                // If you call reload here, you can run into a Core Data crash,
                                // where you see [__NSArrayM insertObject:atIndex:]: object cannot be nil.
                                // To be honest, I'm not sure what this is, could be a bug.
                                // [self.collectionView     :@[indexPath]];

                                // Instead, use reload here.
                                [self.dataSourceDelegate configureCell:[self.collectionView cellForItemAtIndexPath:indexPath]
                                                           atIndexPath:indexPath];
                                break;
                            case NSFetchedResultsChangeMove:
                                [self.collectionView moveItemAtIndexPath:indexPath[0] toIndexPath:indexPath[1]];
                                break;
                        }
                    }];
                }
            } completion:nil];
        }
        
        [self.sectionChanges removeAllObjects];
        [self.objectChanges removeAllObjects];
    }
}

- (BOOL)shouldReloadCollectionViewToPreventKnownIssue
{
    __block BOOL shouldReload = NO;
    for (NSDictionary *change in self.objectChanges) {
        [change enumerateKeysAndObjectsUsingBlock:^(id key, id obj, BOOL *stop) {
            NSFetchedResultsChangeType type = [key unsignedIntegerValue];
            NSIndexPath *indexPath = obj;
            switch (type) {
                case NSFetchedResultsChangeInsert:
                    if ([self.collectionView numberOfItemsInSection:indexPath.section] == 0) {
                        shouldReload = YES;
                    } else {
                        shouldReload = NO;
                    }
                    break;
                case NSFetchedResultsChangeDelete:
                    if ([self.collectionView numberOfItemsInSection:indexPath.section] == 1) {
                        shouldReload = YES;
                    } else {
                        shouldReload = NO;
                    }
                    break;
                case NSFetchedResultsChangeUpdate:
                    shouldReload = NO;
                    break;
                case NSFetchedResultsChangeMove:
                    shouldReload = NO;
                    break;
            }
        }];
    }
    return shouldReload;
}

@end