使用 UICollectionView 和 NSFetchedResultsController

Question

我正在使用在 github 上找到的一个项目，它允许我使用 NSFetchedResultsController 和 UICollectionView，该项目是 this

但是当我像这样保存一个新对象时：

NSManagedObject *doc = [NSEntityDescription insertNewObjectForEntityForName:@"Document" inManagedObjectContext:self.managedObjectContext];
                    [doc setValue:[title contents] forKey:@"docName"];
[doc setValue:element valueforKey:@"Element"]

[self saveContext];

我收到此错误：

 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)

我已尝试删除该项目，并且保存有效，所以我认为该项目存在问题，有什么帮助吗？

Answer 1

我建议您导出 NSManagedObject 子类并如下声明您的对象：

// At top of the file:
#import "Document.h"

// In your Method:
Document *doc = (Document *)[NSEntityDescription insertNewObjectForEntityForName:@"Document" inManagedObjectContext:self.managedObjectContext];
doc.docName = title.contents;

NSError *error = nil;
[self.managedObjectContext save:&error];

if (error != nil) {
    NSLog(@"Oh no! Something terrible happened! Error: %@", error);
}
else {
    NSLog(@"Saved! Yay!");
}