I have multiple sections in my UICollectionView grouped by "datasetType".
I also have a custom UICollectionViewCell for each section.
How can I determine which custom UICollectionViewCell I need in the cellForItemAtIndexPath method?
My first though was go to based of the [sectionInfo name]:
id sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:indexPath.section];
if ([[sectionInfo name] isEqualToString:@"DatasetA"]) {
DatasetACell *datasetACell = [collectionView dequeueReusableCellWithReuseIdentifier:datasetACellIdentifer forIndexPath:indexPath];
DatasetA *datasetA = [self.fetchedResultsController objectAtIndexPath:indexPath];
}
But I'm running to an issue where its trying to load the wrong dataset cell.
Should this work and I need to look else where for the error? Or am I doing this part wrong?
EDIT:
What I have should work. The issue is the index's do not line up.
For my fetchedResultsController, I create it as:
_fetchedResultsController = [Dataset MR_fetchAllSortedBy:NAME
ascending:TRUE
withPredicate:predicate
groupBy:@"datasetType"
delegate:self.fetchedResultsController.delegate
inContext:[NSManagedObjectContext MR_contextForCurrentThread]];
This fetches them and sorts them by name. I use Magical Record in the project, and I use its fetch controller cause I can not get the Core Data fetch controller to work:
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Dataset" inManagedObjectContext:[NSManagedObjectContext MR_contextForCurrentThread]];
[fetchRequest setEntity:entity];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:NAME ascending:TRUE selector:@selector(caseInsensitiveCompare:)];
NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
NSError *error;
NSArray *fetchedArray = [[NSManagedObjectContext MR_contextForCurrentThread] executeFetchRequest:fetchRequest error:&error];
NSLog(@"fetchedArray: %@", fetchedArray);
NSFetchedResultsController *FRC = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:[NSManagedObjectContext MR_contextForCurrentThread] sectionNameKeyPath:nil cacheName:nil];
FRC.delegate = self;
The fetchRequest I do in this code returns the entities, its once I put it through the fetch controller it always returns nothing. I don't think it likes MR's context. /boggle
When I try to fill each subclassed UICollectionViewCell (DatasetACell, DataseetBCell, etc), it can retrieve the wrong data cell.
So at indexPath (0,0), in the NSFetchedResultsController
[self.fetchedResultsController sections] objectAtIndex:indexPath]
will return a datasetA entity while the collection view for the same index
[collectionView dequeueReusableCellWithReuseIdentifier:datasetACell forIndexPath:indexPath]
returns a datasetBCell.
There is an issue with the NSFetchedResultsController is sorted while the [collectionView dequeueResuableCellwithReuseIdentifier:forIndexPath] is not sorted.
Full code:
-(NSFetchedResultsController *)fetchedResultsController {
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"boundary.boundaryID == %@", self.dataseter.boundaryID];
_fetchedResultsController = [Dataset MR_fetchAllSortedBy:NAME
ascending:TRUE
withPredicate:predicate
groupBy:@"datasetType"
delegate:_fetchedResultsController.delegate
inContext:[NSManagedObjectContext MR_contextForCurrentThread]];
return _fetchedResultsController;
}
-(UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath {
id sectionInfo = [[self.fetchedResultsController sections] objectAtIndex:indexPath.section];
NSLog(@"indexPath: %@", indexPath);
NSLog(@"[sectionInfo name]: %@", [sectionInfo name]);
if ([[sectionInfo name] isEqualToString:SAVED_ANALYSIS]) {
NSLog(@"section name is DATASET A");
DatasetCellA *datasetCellA = (DatasetCellA *)[collectionView dequeueReusableCellWithReuseIdentifier:datasetcellAIdentifier forIndexPath:indexPath];
DatasetA *datasetA = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSLog(@"datasetA.id: %@", datasetA.id);
NSLog(@"datasetA: %@", datasetA);
// configure and return cell
}
else if ([[sectionInfo name] isEqualToString:EDITED_IMAGES]) {
NSLog(@"section name is DATASET B");
DatasetCellB *datasetCellB = (DatasetCellB *)[collectionView dequeueReusableCellWithReuseIdentifier:datasetCellBIdentifer forIndexPath:indexPath];
DatasetB *datasetB = [self.fetchedResultsController objectAtIndex:indexPath];
NSLog(@"editedImage.id: %@", datasetB.id);
NSLog(@"editedImage: %@", datasetB);
// configure and return cell
}
}
LOG:
2013-04-04 10:59:38.697 [2380:14003] indexPath: <NSIndexPath 0x19b645c0> 2 indexes [0, 0]
2013-04-04 10:59:38.697 [2380:14003] [sectionInfo name]: Dataset B
2013-04-04 10:59:38.697 [2380:14003] section name is DATASET B
2013-04-04 10:59:38.702 [2380:14003] datasetB.id: 1581
2013-04-04 10:59:38.703 [2380:14003] datasetB: <DatasetA: 0x1c193ac0> (entity: DatasetA; id: 0x16141bd0 <x-coredata://9313C8D3-0AA8-4F3F-B32D-F1F7843D4FA1/DatasetA/p168> ; data: {
})
2013-04-04 10:59:38.703 [2380:14003] indexPath: <NSIndexPath 0x19b64560> 2 indexes [1, 0]
2013-04-04 10:59:38.703 [2380:14003] [sectionInfo name]: Dataset A
2013-04-04 10:59:38.704 [2380:14003] section name is DATSET A
2013-04-04 10:59:38.709 [2380:14003] datasetA.id: 75
2013-04-04 10:59:38.709 [2380:14003] datasetA: <DatasetB: 0x1c15a830> (entity: DatasetB; id: 0x16141b30 <x-coredata://9313C8D3-0AA8-4F3F-B32D-F1F7843D4FA1/DatasetB/p165> ; data: {
})
2013-04-04 10:59:38.724 [2380:14003] -[DatasetB mode]: unrecognized selector sent to instance 0x1c15a830
2013-04-04 10:59:38.725 [2380:14003] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[DatasetB mode]: unrecognized selector sent to instance 0x1c15a830'
*** First throw call stack:
(0x1c19012 0x1a3ee7e 0x1ca44bd 0x1c08bbc 0x1c0894e 0x80028 0xe862da 0xe878f4 0xe89b91 0x9d32dd 0x1a526b0 0x56cfc0 0x56133c 0x561150 0x4df0bc 0x4e0227 0x4e08e2 0x1be1afe 0x1be1a3d 0x1bbf7c2 0x1bbef44 0x1bbee1b 0x28cc7e3 0x28cc668 0x982ffc 0x1ebd 0x1de5)
libc++abi.dylib: terminate called throwing an exception
For the first index (0,0), the code thinks it is a DatasetB but is actually a DatasetA. In the second index (1,0) its the opposite; the code thinks its a DatasetA but is a DatasetB. In this set, there is 1 DatasetB and many DatasetA's.
When the fetch controller sorts it, it sorts Dataset B first. The collection view is expecting a DatasetB but the fetch controller is returning a DatasetA for the same index.
It appears there is an issue with the sorting which needs to be sorted.
But my question is why are you switching on the section name? Why not just switch on the class of the item?
id object = [self.fetchedResultsController objectAtIndexPath:indexPath];
if ([object isKindOfClass:[DatasetA class]] {
// Do your DatasetCellA stuff
} else if ([object isKindOfClass:[DatasetB class]) {
// Do your DatasetCellB stuff
}
At least this way you don't have issues with the sorting
You probably want to correct your fetch request so that you sort by datasetType and then by name.
- (NSFetchedResultsController *)fetchedResultsController
{
if (!_fetchedResultsController) {
return _fetchedResultsController;
}
NSFetchRequest *request = [[NSFetchRequest alloc] init];
request.entity = [Dataset MR_entityDescription];
request.sortDescriptors = @[
[NSSortDescriptor sortDescriptorWithKey:@"datasetType" ascending:YES],
[NSSortDescriptor sortDescriptorWithKey:@"name" ascending:NO],
];
_fetchedResultsController =
[[NSFetchedResultsController alloc] initWithFetchRequest:request
managedObjectContext:[NSManagedObjectContext MR_context]
sectionNameKeyPath:@"datasetType"
cacheName:nil];
NSError *error = nil;
if (![_fetchedResultsController performFetch:&error]) {
NSLog(@"Could not perform fetch %@", [error localizedDescription]);
}
_fetchedResultsController.delegate = <..your delegate..>;
return _fetchedResultsController;
}
Also the reason your self made fetchResultsController probably returned nothing is because you don't perform the fetch with the fetch request yourself, you do it through the fetchedResultsController like
if ([fetchedResultsController performFetch:&error]) {
//...
Without more knowledge of the model structure I can't be more certain, but here goes...
I think your problem is that you expect the search results to be sorted a certain way, but they're not sorted in the way you expect them.
The dataset is using a groupBy:@"datasetType" clause, which defines the sections. But the sections will also be sorted implicitly by the groupBy key. So the question is:
What is this datasetType key in your model, and is it what you expect it to be? Clearly you want to sort by dataset name, but is datasetType what the name is? This is where I believe the problem lies. You're retrieving the wrong sort order because you're not grouping by the dataset's name.
PS: you have "DATSET A" and "DATASET B"... So if you are indeed grouping by the dataset name, it is all working as expected... except for your names which have typos.
You apparently have a typo in your dataset names:
2013-04-04 10:59:38.704 [2380:14003] section name is DATSET A
With the second 'A' missing in DATSET A, this will sort after DATASET B.
The hazards of literals.
来源：https://stackoverflow.com/questions/15668616/uicollectionview-with-multiple-subclassed-uicollectionviewcell