我有一个名为Location
的数据模型。我使用这些作为UICollectionViewController
中的部分标题。每个location
都可以在这些部分中显示items
。我想在 viewForSupplementaryElementOfKind
中自定义我的部分标题。但是我不知道如何从这种方法中获取正确的Location
对象。
我尝试过这样的事情:
-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.fetchedResultsController sections] [indexPath.section];
Item *item = sectionInfo.objects[0];
Location *location = item.location;
SectionHeaderView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader withReuseIdentifier:@"SectionHeader" forIndexPath:indexPath];
headerView.label.text = location.name;
[...]
但我不断得到:
Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[__NSArrayM objectAtIndex:]: index 0 beyond bounds for empty array'
这可能是因为位置可能没有任何项目。关于我应该怎么做还有其他想法吗?
您的代码看起来非常正确,并且在我的小型测试应用程序中按预期工作。因此,我假设数据源方法中存在一些错误。
这是我使用的:
-(NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return [[self.frc sections] count];
}
-(NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.frc sections][section];
return [sectionInfo numberOfObjects];
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CellView *cell = [collectionView dequeueReusableCellWithReuseIdentifier:@"CellView" forIndexPath:indexPath];
Item *item = [self.frc objectAtIndexPath:indexPath];
cell.name.text = item.name;
return cell;
}
-(UICollectionReusableView *)collectionView:(UICollectionView *)collectionView viewForSupplementaryElementOfKind:(NSString *)kind atIndexPath:(NSIndexPath *)indexPath
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.frc sections][indexPath.section];
Item *item = sectionInfo.objects[0];
Location *location = item.location;
HeaderView *headerView = [collectionView dequeueReusableSupplementaryViewOfKind:UICollectionElementKindSectionHeader
withReuseIdentifier:@"HeaderView" forIndexPath:indexPath];
headerView.title.text = location.name;
return headerView;
}
提取的结果控制器的创建方式如下:
- (NSFetchedResultsController *)frc
{
if (_frc == nil ) {
NSFetchRequest *fetchRequest = [NSFetchRequest fetchRequestWithEntityName:@"Item"];
NSSortDescriptor *sort1 = [[NSSortDescriptor alloc] initWithKey:@"location.name" ascending:NO];
NSSortDescriptor *sort2 = [[NSSortDescriptor alloc] initWithKey:@"name" ascending:NO];
NSArray *sortDescriptors = @[sort1, sort2];
[fetchRequest setSortDescriptors:sortDescriptors];
_frc = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:self.context
sectionNameKeyPath:@"location.name"
cacheName:nil];
NSError *error;
_frc.delegate = self;
[_frc performFetch:&error];
}
return _frc;
}
备注:使用提取的结果控制器自动更新集合视图很棘手,所以这篇文章
http://ashfurrow.com/blog/how-to-use-nsfetchedresultscontroller-with-uicollectionview
(带有代码示例)可能会很有趣。