在UICollectionView中执行insertItemsAtIndexPaths时，我遇到了以下错误：
断言失败:
-[UICollectionViewData indexPathForItemAtGlobalIndex:],
/SourceCache/UIKit/UIKit-2372/UICollectionViewData.m:442
2012-09-26 18:12:34.432
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException',
reason: 'request for index path for global index 805306367
when there are only 1 items in the collection view'
我已经检查过，我的数据源只包含一个元素。 有什么见解，为什么会发生这种情况？如果需要更多信息，我肯定可以提供。
当我向集合视图插入第一个单元格时，我遇到了同样的问题。通过更改代码，我调用了UICollectionView来解决这个问题。
- (void)reloadData
在插入第一个单元格时使用该方法，但是
- (void)insertItemsAtIndexPaths:(NSArray *)indexPaths
在插入所有其他单元格时。
有趣的是，我也遇到了一个问题，那就是
- (void)deleteItemsAtIndexPaths:(NSArray *)indexPaths
当删除最后一个单元格时，我与之前做的一样：只需在删除最后一个单元格时调用reloadData.
在插入单元格之前插入第0个section似乎能让UICollectionView更加稳定。
NSArray *indexPaths = /* indexPaths of the cells to be inserted */
NSUInteger countBeforeInsert = _cells.count;
dispatch_block_t updates = ^{
if (countBeforeInsert < 1) {
[self.collectionView insertSections:[NSIndexSet indexSetWithIndex:0]];
}
[self.collectionView insertItemsAtIndexPaths:indexPaths];
};
[self.collectionView performBatchUpdates:updates completion:nil];
numberOfSectionsInCollectionView:方法的返回值。如果你的集合为空，则返回0个部分，如果集合不为空，则返回1个部分。如果您没有实现此方法或返回0，则在插入后会出现“无效更新”错误，抱怨部分数量不正确。 - nrj我在这里提供了解决此问题的方法：https://gist.github.com/iwasrobbed/5528897
在你的.m文件顶部的私有类别中：
@interface MyViewController ()
{
BOOL shouldReloadCollectionView;
NSBlockOperation *blockOperation;
}
@end
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
shouldReloadCollectionView = NO;
blockOperation = [NSBlockOperation new];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id<NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
__weak UICollectionView *collectionView = self.collectionView;
switch (type) {
case NSFetchedResultsChangeInsert: {
[blockOperation addExecutionBlock:^{
[collectionView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex]];
}];
break;
}
case NSFetchedResultsChangeDelete: {
[blockOperation addExecutionBlock:^{
[collectionView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex]];
}];
break;
}
case NSFetchedResultsChangeUpdate: {
[blockOperation addExecutionBlock:^{
[collectionView reloadSections:[NSIndexSet indexSetWithIndex:sectionIndex]];
}];
break;
}
default:
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath
{
__weak UICollectionView *collectionView = self.collectionView;
switch (type) {
case NSFetchedResultsChangeInsert: {
if ([self.collectionView numberOfSections] > 0) {
if ([self.collectionView numberOfItemsInSection:indexPath.section] == 0) {
shouldReloadCollectionView = YES;
} else {
[blockOperation addExecutionBlock:^{
[collectionView insertItemsAtIndexPaths:@[newIndexPath]];
}];
}
} else {
shouldReloadCollectionView = YES;
}
break;
}
case NSFetchedResultsChangeDelete: {
if ([self.collectionView numberOfItemsInSection:indexPath.section] == 1) {
shouldReloadCollectionView = YES;
} else {
[blockOperation addExecutionBlock:^{
[collectionView deleteItemsAtIndexPaths:@[indexPath]];
}];
}
break;
}
case NSFetchedResultsChangeUpdate: {
[blockOperation addExecutionBlock:^{
[collectionView reloadItemsAtIndexPaths:@[indexPath]];
}];
break;
}
case NSFetchedResultsChangeMove: {
[blockOperation addExecutionBlock:^{
[collectionView moveItemAtIndexPath:indexPath toIndexPath:newIndexPath];
}];
break;
}
default:
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
// Checks if we should reload the collection view to fix a bug @ http://openradar.appspot.com/12954582
if (shouldReloadCollectionView) {
[self.collectionView reloadData];
} else {
[self.collectionView performBatchUpdates:^{
[blockOperation start];
} completion:nil];
}
}
NSFetchedResultsChangeInsert中的if子句应该检查*new*IndexPath.section部分中的项目数量。 - Simon WhitakercollectionView:viewForSupplementaryElementOfKind:atIndexPath:返回一个有效的或空的补充视图。在遇到崩溃后，我检查了文档，以下是文档中的说明：
这个方法必须始终返回一个有效的视图对象。如果您不想在特定情况下使用补充视图，则布局对象不应为该视图创建属性。或者，您可以通过将相应属性的hidden属性设置为YES或将属性的alpha属性设置为0来隐藏视图。要在流式布局中隐藏头部和底部视图，还可以将这些视图的宽度和高度设置为0。
虽然还有其他方法，但最快的方法似乎是：
- (CGSize)collectionView:(UICollectionView *)collectionView layout:(UICollectionViewFlowLayout *)collectionViewLayout referenceSizeForHeaderInSection:(NSInteger)section {
return <condition> ? collectionViewLayout.headerReferenceSize : CGSizeZero;
}
我的集合视图从两个数据源获取项目，更新它们会导致这个问题。我的解决方法是将数据更新和集合视图重新加载排队：
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
//Update Data Array
weakSelf.dataProfile = [results lastObject];
//Reload CollectionView
[weakSelf.collectionView reloadItemsAtIndexPaths:@[[NSIndexPath indexPathForItem:0 inSection:0]]];
}];
NSIndexPath的方式上。例如，要删除第三个单元格，而不是执行以下操作：NSIndexPath* indexPath = [NSIndexPath indexPathWithIndex:2];
[_collectionView deleteItemsAtIndexPaths:@[indexPath]];
NSIndexPath* indexPath = [NSIndexPath indexPathForItem:2 inSection:0];
[_collectionView deleteItemsAtIndexPaths:@[indexPath]];
请确保在numberOfSectionsInCollectionView:方法中返回正确的值。
我用来计算段落的值是空的，因此有0个段落。这导致了异常。
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView {
NSInteger sectionCount = self.objectThatShouldHaveAValueButIsActuallyNil.sectionCount;
// section count is wrong!
return sectionCount;
}
请检查在UICollectionViewDataSource方法中是否返回了正确数量的元素：
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
和
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
UICollectionViewFlowLayout 或从其派生的布局），而且在插入/移动之前该部分有0个单元格时，就会发生问题。- (NSInteger)collectionView:(UICollectionView *)view numberOfItemsInSection:(NSInteger)section 返回该区域实际单元格数量加 1，其中包括标题视图。在 - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath 中返回：
if ((indexPath.section == YOUR_SECTION_WITH_THE_HEADER_VIEW) && (indexPath.item == [self collectionView:collectionView numberOfItemsInSection:indexPath.section] - 1)) {
cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"EmptyCell" forIndexPath:indexPath];
}
... 用于该位置的空单元格。请记得在 viewDidLoad 或任何初始化 UICollectionView 的地方注册单元格重用：
[self.collectionView registerClass:[UICollectionReusableView class] forCellWithReuseIdentifier:@"EmptyCell"];
moveItemAtIndexPath: 或 insertItemsAtIndexPaths: 而不崩溃。这是我在项目中使用的解决此错误的方法，我想在这里发布，以防有人觉得有价值。
@interface FetchedResultsViewController ()
@property (nonatomic) NSMutableIndexSet *sectionsToAdd;
@property (nonatomic) NSMutableIndexSet *sectionsToDelete;
@property (nonatomic) NSMutableArray *indexPathsToAdd;
@property (nonatomic) NSMutableArray *indexPathsToDelete;
@property (nonatomic) NSMutableArray *indexPathsToUpdate;
@end
#pragma mark - NSFetchedResultsControllerDelegate
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
[self resetFetchedResultControllerChanges];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
switch(type)
{
case NSFetchedResultsChangeInsert:
[self.sectionsToAdd addIndex:sectionIndex];
break;
case NSFetchedResultsChangeDelete:
[self.sectionsToDelete addIndex:sectionIndex];
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
switch(type)
{
case NSFetchedResultsChangeInsert:
[self.indexPathsToAdd addObject:newIndexPath];
break;
case NSFetchedResultsChangeDelete:
[self.indexPathsToDelete addObject:indexPath];
break;
case NSFetchedResultsChangeUpdate:
[self.indexPathsToUpdate addObject:indexPath];
break;
case NSFetchedResultsChangeMove:
[self.indexPathsToAdd addObject:newIndexPath];
[self.indexPathsToDelete addObject:indexPath];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
if (self.sectionsToAdd.count > 0 || self.sectionsToDelete.count > 0 || self.indexPathsToAdd.count > 0 || self.indexPathsToDelete > 0 || self.indexPathsToUpdate > 0)
{
if ([self shouldReloadCollectionViewFromChangedContent])
{
[self.collectionView reloadData];
[self resetFetchedResultControllerChanges];
}
else
{
[self.collectionView performBatchUpdates:^{
if (self.sectionsToAdd.count > 0)
{
[self.collectionView insertSections:self.sectionsToAdd];
}
if (self.sectionsToDelete.count > 0)
{
[self.collectionView deleteSections:self.sectionsToDelete];
}
if (self.indexPathsToAdd.count > 0)
{
[self.collectionView insertItemsAtIndexPaths:self.indexPathsToAdd];
}
if (self.indexPathsToDelete.count > 0)
{
[self.collectionView deleteItemsAtIndexPaths:self.indexPathsToDelete];
}
for (NSIndexPath *indexPath in self.indexPathsToUpdate)
{
[self configureCell:[self.collectionView cellForItemAtIndexPath:indexPath]
atIndexPath:indexPath];
}
} completion:^(BOOL finished) {
[self resetFetchedResultControllerChanges];
}];
}
}
}
// 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.
// https://dev59.com/Smcs5IYBdhLWcg3wu2jS
// This code should be removed once the bug has been fixed, it is tracked in OpenRadar
// http://openradar.appspot.com/12954582
- (BOOL)shouldReloadCollectionViewFromChangedContent
{
NSInteger totalNumberOfIndexPaths = 0;
for (NSInteger i = 0; i < self.collectionView.numberOfSections; i++)
{
totalNumberOfIndexPaths += [self.collectionView numberOfItemsInSection:i];
}
NSInteger numberOfItemsAfterUpdates = totalNumberOfIndexPaths;
numberOfItemsAfterUpdates += self.indexPathsToAdd.count;
numberOfItemsAfterUpdates -= self.indexPathsToDelete.count;
BOOL shouldReload = NO;
if (numberOfItemsAfterUpdates == 0 && totalNumberOfIndexPaths == 1)
{
shouldReload = YES;
}
if (numberOfItemsAfterUpdates == 1 && totalNumberOfIndexPaths == 0)
{
shouldReload = YES;
}
return shouldReload;
}
- (void)resetFetchedResultControllerChanges
{
[self.sectionsToAdd removeAllIndexes];
[self.sectionsToDelete removeAllIndexes];
[self.indexPathsToAdd removeAllObjects];
[self.indexPathsToDelete removeAllObjects];
[self.indexPathsToUpdate removeAllObjects];
}