使用UICollectionView和NSFetchedResultsController不保存
我在github上使用项目查找，让我使用UICollectionView和UICollectionView ，项目是这样的
在我的项目中，我有一个核心数据与两个实体， Element和Document ， Element和Document之间有一对多的关系，所以一个Element可以有更多的Document ，但一个Document只能有一个Element ，然后我这样做AppDelegate ：
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]]; // Override point for customization after application launch. ElementViewController *elementView = [[ElementViewController alloc] initWithNibName:@"ElementViewController" bundle:nil]; elementView.managedObjectContext = self.managedObjectContext; DocumentViewController *documentView = [[DocumentViewController alloc] initWithNibName:@"DocumentViewController" bundle:nil]; documentView.managedObjectContext = self.managedObjectContext; elementView.documentView = documentView; UINavigationController *navController = [[UINavigationController alloc] initWithRootViewController:elementView]; self.window.rootViewController = navController; [self.window makeKeyAndVisible]; return YES; }
这是应用程序委托，然后在ElementViewController我有一个UICollectionView与UICollectionView ，和所有工作正常，当我select一个UICollectionViewCell我打开DocumentViewController ：
- (void)collectionView:(UICollectionView *)collectionView didSelectItemAtIndexPath:(NSIndexPath *)indexPath { self.documentView.element = [self.fetchedResultsController objectAtIndexPath:indexPath]; [self.navigationController pushViewController:self.documentView animated:YES]; }
那么这是我的DocumentViewController.h ：
#import <UIKit/UIKit.h> #import "Element.h" @interface DocumentViewController : UIViewController <NSFetchedResultsControllerDelegate> @property (strong, nonatomic) NSManagedObjectContext *managedObjectContext; @property (weak, nonatomic) IBOutlet UICollectionView *collectionView; @property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController; @property (strong, nonatomic) Element *element; @end
而且在这里，我有NSFetchedResultsController ， Element标题的谓词filter：
- (NSFetchedResultsController *)fetchedResultsController { if (_fetchedResultsController != nil) { return _fetchedResultsController; } NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init]; // Edit the entity name as appropriate. NSEntityDescription *entity = [NSEntityDescription entityForName:@"Document" inManagedObjectContext:self.managedObjectContext]; [fetchRequest setEntity:entity]; // Set the batch size to a suitable number. [fetchRequest setFetchBatchSize:20]; // Edit the sort key as appropriate. NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"docDate" ascending:NO]; NSArray *sortDescriptors = @[sortDescriptor]; [fetchRequest setSortDescriptors:sortDescriptors]; [fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"SUBQUERY(element, $b, $b.name == %@).@count > 0", self.element.name]]; // Edit the section name key path and cache name if appropriate. // nil for section name key path means "no sections". NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:self.managedObjectContext sectionNameKeyPath:nil cacheName:nil]; aFetchedResultsController.delegate = self; self.fetchedResultsController = aFetchedResultsController; NSError *error = nil; if (![self.fetchedResultsController performFetch:&error]) { // Replace this implementation with code to handle the error appropriately. // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development. NSLog(@"Unresolved error %@, %@", error, [error userInfo]); abort(); } return _fetchedResultsController; }
然后我也添加这个：
- (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; [self reloadCollectionView]; [self addDocument]; } - (void)reloadTableView { self.fetchedResultsController = nil; //Because not search every time for different Element NSError *error; if (![[self fetchedResultsController] performFetch:&error]) { NSLog(@"Error in search %@, %@", error, [error userInfo]); } else { [self.collectionView reloadData]; } }
然后在viewWillAppear中有addDocument方法：
- (void)addDocument { Document *document = (Document *)[NSEntityDescription insertNewObjectForEntityForName:@"Document" inManagedObjectContext:self.managedObjectContext]; [document setDocName:[title contents]]; [document setElement:self.element]; //here the app crash }
我收到这些错误：
CoreData: error: Serious application error. Exception was caught during Core Data change processing. This is usually a bug within an observer of NSManagedObjectContextObjectsDidChangeNotification. Can't perform collection evaluate with non-collection object. with userInfo (null) 2013-01-25 10:28:56.392 App[383:c07] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Can't perform collection evaluate with non-collection object.'
任何人都可以帮助我？
编辑：这是NSManagedObjectClass：
#import <Foundation/Foundation.h> #import <CoreData/CoreData.h> @class Document; @interface Element : NSManagedObject @property (nonatomic, retain) NSString * dateFormat; @property (nonatomic, retain) NSString * dateFormat2; @property (nonatomic, retain) id img; @property (nonatomic, retain) NSDate * imgDate; @property (nonatomic, retain) NSString * imgUrl; @property (nonatomic, retain) NSString * language; @property (nonatomic, retain) NSString * name; @property (nonatomic, retain) NSString * name2; @property (nonatomic, retain) NSString * pathDocuments; @property (nonatomic, retain) NSNumber * releaseDateWeek; @property (nonatomic, retain) NSNumber * type; @property (nonatomic, retain) NSSet *documents; @end @interface Element (CoreDataGeneratedAccessors) - (void)addDocumentsObject:(Document *)value; - (void)removeDocumentsObject:(Document *)value; - (void)addDocuments:(NSSet *)values; - (void)removeDocuments:(NSSet *)values; @end @interface ImageToDataTransformer : NSValueTransformer { } @end Document.h #import <Foundation/Foundation.h> #import <CoreData/CoreData.h> @class Element; @interface Document : NSManagedObject @property (nonatomic, retain) NSDate * docDate; @property (nonatomic, retain) id docImage; @property (nonatomic, retain) NSString * docName; @property (nonatomic, retain) NSString * docPath; @property (nonatomic, retain) NSNumber * docSize; @property (nonatomic, retain) NSString * docUrl; @property (nonatomic, retain) NSNumber * isDownloading; @property (nonatomic, retain) NSNumber * isStored; @property (nonatomic, retain) NSNumber * pageNumber; @property (nonatomic, retain) NSString * password; @property (nonatomic, retain) NSNumber * progressBar; @property (nonatomic, retain) Element *element; @end
问题看起来是这样的：
[fetchRequest setPredicate:[NSPredicate predicateWithFormat:@"SUBQUERY(element, $b, $b.name == %@).@count > 0", self.element.name]];
“元素”不会parsing为一个集合（按照SUBQUERY的要求），而仅仅是一个对象。
请参阅： http : //developer.apple.com/library/Mac/#documentation/Cocoa/Reference/Foundation/Classes/NSExpression_Class/Reference/NSExpression.html