nsmanagedobjectcontext

问题 I want to use the singleton UIApplication to access the managedObjectContext of the AppDelegate. But when I write [[[UIApplication sharedApplication] delegate] managedObjectContext] or [[[UIApplication sharedApplication] delegate] __managedObjectContext] it doesn't work. But this line works fine : NSLog(@"Seeking for the AppDelegate : %@", [[[UIApplication sharedApplication] delegate] class]); Do you have a solution ? Niels 回答1: Try casting it to your actual app delegate implementation, like

问题 I have one doubt about multithreading in coredata. if we are using multithreading we should use separate NSManagedObjectContext for inserting new data or updating or else we can use parent child context method. But i am creating new NSManagedObjectContext only. My question is that should i use separate NSManagedObjectContext for even fetching in background thread also. If not (i.e. we can use main queue NSManagedObjectContext only) than why i m getting __psynch_mutexwait error. Thanks, 回答1:

问题 I have around 10000 objects of entity ' Message '. When I add a new ' Message ' i want to first see whether it exists - and if it does just update it's data, but if it doesn't to create it. Right now the "find-or-create" algorithm works with by saving all of the Message objects ' objectID ' in one array and then filtering through them and getting the messages with existingObjectWithID:error: This works fine but in my case when I fetch an 'Message' using existingObjectWithID : and then try to

问题 The documentation says: - (void)reset Returns the receiver to its base state. Discussion All the receiver's managed objects are “forgotten.” If you use this method, you should ensure that you also discard references to any managed objects fetched using the receiver, since they will be invalid afterwards. - (void)rollback Removes everything from the undo stack, discards all insertions and deletions, and restores updated objects to their last committed values. Discussion This method does not

问题 In core data for the iPhone, I was getting all sorts of errors trying to save data to a NSManagedObjectContext . I believe that my issues were all to do with me using a NSManagedObjectContext that was being used in multiple threads. So I wanted to create a new NSManagedObjectContext and try that, but I cannot find the example code to simply create a new instance... I know its simple, but I would really appreciate any help here. Note, I have seen this article on the Apple docs: http:/

问题 I am mapping Json Data from Server using Restkit and I am Displaying those data by fetching from db. There is a refresh button in my view which performs the above operation again. Scenario: I have two tables Key & Profile which has one-one relationship. I am fetching data from DB using follwing code NSFetchRequest *fetchRequest = [Key fetchRequest]; [fetchRequest setRelationshipKeyPathsForPrefetching:[NSArray arrayWithObject:@"Profile"]]; [fetchRequest setIncludesSubentities:YES]; NSArray

问题 My app sometimes inserts objects into the managed object context that are not meant to necessarily be saved. For example, when I launch an 'add entity' modal, I create a managed object and assign it to the modal. If the user saves from that modal, I save the context. If he cancels, I delete the object and no save is necessary. I have now introduced an 'import' feature that switches to my app (using a URL scheme) and adds an entity. Because one of these modals might be open, it is not safe to

问题 I've enabled com.apple.CoreData.ConcurrencyDebug 1 to check Core Data concurrency errors. I have the following code snippet in a Swift class: lazy var context: NSManagedObjectContext! = { var appDelegate = UIApplication.sharedApplication().delegate as! AppDelegate return appDelegate.managedObjectContext! }() func getAllEntitiesToRootContext() -> [MyEntity]? { let fetchRequest = NSFetchRequest(entityName:"MyEntity") do { let fetchedResults = try context.executeFetchRequest(fetchRequest) as!

问题 I have two NSManagedObjectContext which are independent: there is no relationship between the two. How to synchronize the two in Core Data? 回答1: Yes you can do that if you are having two context like on is in background thread and other is on main thread for example then you can use mergeChangesFromContextDidSaveNotification to synchronize the data of two managed object context // MARK: - // MARK: Notification Handling func managedObjectContextDidSave(notification: NSNotification) { dispatch

问题 I have an app where the PersistentStoreCoordinator is set up within AppDelegate. I want to load a new sqlite database from a list of saved sqlite files. I'm happy with deleting the existing Persistent Store and sqlite file and replacing the sqlite file with the one loaded from the table. However, how do I reload/refresh the PersistentStoreCoordinator from the ViewController action of selecting the new file? I've tried setting AppDelegate as a delegate of the ViewController, but this seems to