我的 UICollectionView 中有多个部分按“datasetType”分组。

我也有每个部分的自定义 UICollectionViewCell。

如何在 cellForItemAtIndexPath 方法中确定我需要哪个自定义 UICollectionViewCell？

我的第一个想法是基于 [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];
}

但我遇到了一个问题，它试图加载错误的数据集单元格。

这应该有效吗？我需要在其他地方寻找错误吗？还是我这部分做错了？

编辑:

我所拥有的应该可以工作。问题是索引没有对齐。

对于我的 fetchedResultsController，我将其创建为:

_fetchedResultsController = [Dataset MR_fetchAllSortedBy:NAME
                                               ascending:TRUE
                                           withPredicate:predicate
                                                 groupBy:@"datasetType"
                                                delegate:self.fetchedResultsController.delegate
                                               inContext:[NSManagedObjectContext MR_contextForCurrentThread]];

这会获取它们并按名称对它们进行排序。我在项目中使用了 Magical Record，并且我使用了它的获取 Controller ，因为我无法让 Core Data 获取 Controller 工作:

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;

我在这段代码中执行的 fetchRequest 返回实体，一旦我将它放入 fetch Controller ，它总是不返回任何内容。我认为它不喜欢 MR 的语境。/难以置信

当我尝试填充每个子类 UICollectionViewCell(DatasetACell、DataseetBCell 等)时，它可能会检索到错误的数据单元格。

所以在 NSFetchedResultsController 中的 indexPath (0,0)

[self.fetchedResultsController sections] objectAtIndex:indexPath]

将返回一个datasetA实体，而collection view为相同的索引

[collectionView dequeueReusableCellWithReuseIdentifier:datasetACell forIndexPath:indexPath] 

返回一个数据集BCell。

NSFetchedResultsController 排序时出现问题，而 [collectionView dequeueResuableCellwithReuseIdentifier:forIndexPath] 未排序。

完整代码:

-(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
    }
}

日志:

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

对于第一个索引 (0,0)，代码认为它是 DatasetB 但实际上是 DatasetA。在第二个索引 (1,0) 中则相反；代码认为它是一个 DatasetA 但实际上是一个 DatasetB。在这个集合中，有 1 个 DatasetB 和许多 DatasetA。

当获取 Controller 对其进行排序时，它首先对数据集 B 进行排序。 Collection View 需要一个 DatasetB，但获取 Controller 正在为同一索引返回一个 DatasetA。

最佳答案

看来排序有问题，需要排序。

但我的问题是，您为什么要打开版 block 名称？为什么不直接打开项目的类别？

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
}

至少这样你在排序时没有问题

您可能想更正您的提取请求，以便按 datasetType 排序，然后按 name 排序。

- (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;
}

另外，您自制的 fetchResultsController 可能没有返回任何内容的原因是因为您没有自己使用提取请求执行提取，而是通过 fetchedResultsController 来完成

if ([fetchedResultsController performFetch:&error]) {
   //...

关于ios - 具有多个子类 UICollectionViewCell 的 UICollectionView，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/15668616/