我正在使用Core Data委托方法来更新我的UICollectionView。
即使代码中的所有内容都显示正常，我也会收到此错误：
2014-03-28 22:27:07.196 Magin[5387:60b] CoreData: error: Serious application error. An exception was caught from the delegate of NSFetchedResultsController during a call to
-controllerDidChangeContent:. Invalid update: invalid number of items in section 0. The number of items contained in an existing section
after the update (8) must be equal to the number of items contained in
that section before the update (8), plus or minus the number of items
inserted or deleted from that section (8 inserted, 0 deleted) and plus
or minus the number of items moved into or out of that section (0
moved in, 0 moved out). with userInfo (null)
以下是更新代码：
- (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;
}
[_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;
}
[_objectChanges addObject:change];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
if ([_sectionChanges count] > 0)
{
[self.collectionView performBatchUpdates:^{
for (NSDictionary *change in _sectionChanges)
{
[change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) {
NSFetchedResultsChangeType type = [key unsignedIntegerValue];
switch (type)
{
case NSFetchedResultsChangeInsert:
[self.collectionView insertSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]]];
break;
case NSFetchedResultsChangeDelete:
[self.collectionView deleteSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]]];
break;
case NSFetchedResultsChangeUpdate:
[self.collectionView reloadSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]]];
break;
}
}];
}
} completion:nil];
}
if ([_objectChanges count] > 0 && [_sectionChanges count] == 0)
{
if ([self shouldReloadCollectionViewToPreventKnownIssue] || self.collectionView.window == nil) {
// 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 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 _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;
}
_objectChanges和_secitonChanges是NSMutableArray类型的对象。