Merge pull request #7 from cwagdev/master

Known bug in UICollectionView causes exceptions and odd behaviors
ashfurrow · Feb 18, 2013 · eaf0af0 · eaf0af0
2 parents 3d4b848 + c38fcc2
commit eaf0af0
Showing 1 changed file with 70 additions and 24 deletions.
diff --git a/AFMasterViewController.m b/AFMasterViewController.m
@@ -176,35 +176,81 @@ - (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
 
     if ([_objectChanges count] > 0 && [_sectionChanges count] == 0)
     {
-        [self.collectionView performBatchUpdates:^{
+
+        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];
 
-            for (NSDictionary *change in _objectChanges)
-            {
-                [change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) {
-
-                    NSFetchedResultsChangeType type = [key unsignedIntegerValue];
-                    switch (type)
-                    {
-                        case NSFetchedResultsChangeInsert:
-                            [self.collectionView insertItemsAtIndexPaths:@[obj]];
-                            break;
-                        case NSFetchedResultsChangeDelete:
-                            [self.collectionView deleteItemsAtIndexPaths:@[obj]];
-                            break;
-                        case NSFetchedResultsChangeUpdate:
-                            [self.collectionView reloadItemsAtIndexPaths:@[obj]];
-                            break;
-                        case NSFetchedResultsChangeMove:
-                            [self.collectionView moveItemAtIndexPath:obj[0] toIndexPath:obj[1]];
-                            break;
+        } else {
+
+            [self.collectionView performBatchUpdates:^{
+
+                for (NSDictionary *change in _objectChanges)
+                {
+                    [change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) {
+
+                        NSFetchedResultsChangeType type = [key unsignedIntegerValue];
+                        switch (type)
+                        {
+                            case NSFetchedResultsChangeInsert:
+                                [self.collectionView insertItemsAtIndexPaths:@[obj]];
+                                break;
+                            case NSFetchedResultsChangeDelete:
+                                [self.collectionView deleteItemsAtIndexPaths:@[obj]];
+                                break;
+                            case NSFetchedResultsChangeUpdate:
+                                [self.collectionView reloadItemsAtIndexPaths:@[obj]];
+                                break;
+                            case NSFetchedResultsChangeMove:
+                                [self.collectionView moveItemAtIndexPath:obj[0] toIndexPath:obj[1]];
+                                break;
+                        }
+                    }];
+                }
+            } completion:nil];
+        }
+
+        [_sectionChanges removeAllObjects];
+        [_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;
             }
-        } completion:nil];
+        }];
     }
 
-    [_sectionChanges removeAllObjects];
-    [_objectChanges removeAllObjects];
+    return shouldReload;
 }
 
 @end