I'm in the progress of updating an existing app for iOS 7 and I've been having some issues with Core Data saving objects. It's a fairly straightforward master-detail style data entry app that uses Core Data for the storage.
When adding a new record I use a second (temporary) managed object context to prevent the record appearing in the list before the record is saved. When a record is added and saved it is visible in the list as expected. However if I exit the app (it doesn't run in the background) and then restart it the record is no longer present. The record is present in the database (visible using the SQLite Manager Firefox plugin anyway), but it just doesn't show in the app.
I've managed to reproduce this using the code that Xcode produces when creating a new project. I've created a new master-detail application and ticked the Use Core Data box to get the example code, then made the following changes:
Add the following to MasterViewController.m
-(void)save:(NSManagedObjectContext*)context
{
if (context != [self.fetchedResultsController managedObjectContext])
{
NSNotificationCenter *dnc = [NSNotificationCenter defaultCenter];
[dnc addObserver:self selector:#selector(addControllerContextDidSave:) name:NSManagedObjectContextDidSaveNotification object:context];
}
NSError *error;
if (![context save:&error])
{
abort();
}
if (context != [self.fetchedResultsController managedObjectContext])
{
NSNotificationCenter *dnc = [NSNotificationCenter defaultCenter];
[dnc removeObserver:self name:NSManagedObjectContextDidSaveNotification object:context];
}
}
- (void)addControllerContextDidSave:(NSNotification*)saveNotification
{
[[self.fetchedResultsController managedObjectContext] mergeChangesFromContextDidSaveNotification:saveNotification];
}
Replace the supplied insertNewObject in insertNewObject with the following to create a new temporary context for adding
- (void)insertNewObject:(id)sender
{
NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
context.persistentStoreCoordinator = [[self.fetchedResultsController managedObjectContext] persistentStoreCoordinator];
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
// If appropriate, configure the new managed object.
// Normally you should use accessor methods, but using KVC here avoids the need to add a custom class to the template.
[newManagedObject setValue:[NSDate date] forKey:#"timeStamp"];
// Save the context.
[self save:context];
}
I also set the app to not run in the background.
If I run this against iOS 6 it behaves as expected i.e. I tap Add and a new record appears, then exit and restart the app and the record is still present.
However if I run the same code against iOS 7 it doesn't work correctly. Tapping Add causes the new record to appear, but if I exit and them restart the app the record is not shown. As mentioned above it is present in the database however.
Interestingly, I've discovered that it might be in some way related to the change in the journaling mode of the SQLite database. If I add the following options in the call to addPersistentStoreWithType I get the expected behaviour running on iOS 7
NSDictionary *options = #{ NSSQLitePragmasOption : #{#"journal_mode" : #"DELETE"} };
So, to the questions (and thanks for reading this far!)
Has anyone else seen this behaviour (or is anyone able to reproduce it based on the description above)?
Is there something wrong with the way I am using a temporary context that I was just lucky with prior to iOS 7, or does this look like an issue with the Core Data framework on iOS 7?
Cheers
Neil
Edit 1:
In answer to Wain's question about saving the main MOC, I was under the impression that this isn't actually necessary because the data is already saved, the merge just updates the already saved changes from the temporary context in to the main context. That said the test code does contain the following methods and saveContext is called on shutdown, however [managedObjectContext hasChanges] returns false so nothing actually gets done at this point
-(void)applicationWillTerminate:(UIApplication *)application
{
// Saves changes in the application's managed object context before the application terminates.
[self saveContext];
}
-(void)saveContext
{
NSError *error = nil;
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil)
{
if ([managedObjectContext hasChanges])
{
if (![managedObjectContext save:&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();
}
}
}
}
It seems to be fixed when you save your main context after merging changes:
- (void)addControllerContextDidSave:(NSNotification*)saveNotification
{
[[self.fetchedResultsController managedObjectContext] mergeChangesFromContextDidSaveNotification:saveNotification];
[self save:[self.fetchedResultsController managedObjectContext]];
}
UPDATE: this error was caused by using cache in NSFetchedResultsController. So, the data isn't lost, it's just not displayed by your NSFetchedResultsController. Further investigation is needed to find out why cache isn't updated when its MOC merges changes, but isn't saved.
Related
Hi I do have a problem with my Core Data storage!
I delete it the following way like I found it here an stack overflow:
NSFetchRequest * allFriends = [[NSFetchRequest alloc] init];
[allFriends setEntity:[NSEntityDescription entityForName:#"Friend" inManagedObjectContext:self.managedObjectContext]];
[allFriends setIncludesPropertyValues:NO]; //only fetch the managedObjectID
NSError * error = nil;
NSArray * friends = [self.managedObjectContext executeFetchRequest:allFriends error:&error];
[allFriends release];
//error handling goes here
for (NSManagedObject * Friend in friends) {
[self.managedObjectContext deleteObject:Friend];
}
this seams to work perfect at runtime!
my tableview (which I manage with NSFetchedResultsController) clears and all is fine it looks!
Also when I hit the home button and start it back up it works.
BUT if I even close it from the multitasking list (so completely close it) and start it back up all is back in the tableView again!
could anybody help me out with this?
Your code is fine but you have forgotten to commit all changes (objects were removed) made to database. So, you should add following lines to your code and after reopening the app your db will not contain that objects:
NSError *error;
if (![self.managedObjectContext save:&error])
{
// Update to handle the
NSLog(#"Unresolved error %#", error);
exit(-1); // Fail
}
Because all changes are stored in memory, don't forget to save the managed object context after some important or critical changes were made. Before you commit your changes, the database/presistent-store file will be in the previously saved state.
Are you saving the managedObjectContext at any point before quitting? Normally you would save the context when the application enters the background or terminates.
I have a simple CoreData app which allows you to add items to a list, displayed in a table view. When the user types in a new item, the following method is called:
- (void)addNewItem:(NSString *)item
{
// Create a new instance of the entity managed by the fetched results controller.
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
Item *newItem = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
[newItem setName:item];
// Save the context.
NSError *error = nil;
if (![context save:&error])
{
//error handling code
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
[context release];
[entity release];
[newItem release];
The app always allows you to add one item to the list, but then crashes if you try to add a second. If I remove "[newItem release];", the app will allow you to add 4 list items, and then suddenly crash when you try to enter a fifth.
The app will only work properly if all three of those release statements at the end of the method are removed. Can anyone explain why?
The objects are all autoreleased (because you never alloc init anything), so you're not supposed to release them yourself. It's not predictable when your app will crash as far as I can tell, but it will eventually crash.
Just to clarify #BoltClock's answer. It's not about alloc, init only, but there's also new..., copy..., etc.
You should read Memory Management Guide, especially Memory Management Rules.
I'm using Core Data + sqlite as a data cache. The app reads in a file into core data, then uses Core Data to run the app. Saves are done to both the NSManagedObjectContext and to the file. I've noticed, though, if I quit the app and reload it without repopulating the Core Data database, some (but not all) of the data saved using -save: is not being saved to the data store.
Changes to my managed object are all done in a single batch on the main thread, with the -save: message being sent after all changes are completed. The data that isn't being saved is a transformable attribute, the only transformable attribute in the core data object. Here's the code that saves the object:
NSInteger columnIndex = [headers indexOfObject:questionID];
if (NSNotFound != columnIndex) {
// parsedLine is a mutable array already
NSMutableArray *parsedLine = person.dataFromFile.parsedLine;
[parsedLine replaceObjectAtIndex:columnIndex withObject:answer];
person.dataFromFile.parsedLine = parsedLine;
person.questionsAnsweredByPerson = [NSNumber numberWithInt:[FileParser questionsAnsweredInRow:person.dataFromFile.parsedLine withRowHeaders:headers]];
person.address.street.questionsAnsweredByPeopleOnStreet = [NSNumber numberWithInt:[self questionsAnsweredByPeopleOnStreet]];
//NSLog(#"rawLineBefore:\n%#", person.dataFromFile.rawLine);
person.dataFromFile.rawLine = [ReconstructCSV composeCSVLineFromArray:person.dataFromFile.parsedLine];
//NSLog(#"rawLineAfter:\n%#", person.dataFromFile.rawLine);
Voter_SurveyAppDelegate *appDelegate = (Voter_SurveyAppDelegate *)[[UIApplication sharedApplication] delegate];
NSError *error;
NSManagedObjectContext *managedObjectContext = [appDelegate managedObjectContext];
if (![managedObjectContext save:&error]) {
// XXX inform the user there was a fatal error opening the file. Low disk space?
NSLog(#"Unresolved error - could not save managedObjectContext - %#, %#", error, [error userInfo]);
abort();
}
return YES;
}
abort(); is not getting called, so I assume -save; is getting called properly.
I doubt it is related, but after this code is run on the main thread, I perform an NSFetchRequest using a new NSManagedObjectContext on a different thread. Nothing else takes place related to Core Data on other threads.
Why isn't the transformable attribute getting saved?
The problem is that transformable properties don't like Mutable objects. As noted in an answer to this question, an NSMutableDictionary wasn't getting saved. In my case, it was an NSMutableArray.
I am using CoreData with iPhone SDK. I am making a notes app. I have a table with note objects displayed from my model. When a button is pressed I want to save the text in the textview to the object being edited. How do I do this? I've been trying several things but none seem to work.
Thanks
EDIT:
NSManagedObjectContext *context = [fetchedResultsController managedObjectContext];
NSEntityDescription *entity = [[fetchedResultsController fetchRequest] entity];
NSManagedObject *newManagedObject = [NSEntityDescription insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
[newManagedObject setValue:detailViewController.textView.text forKey:#"noteText"];
NSError *error;
if (![context save:&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. If it is not possible to recover from the error, display an alert panel that instructs the user to quit the application by pressing the Home button.
*/
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
The above code saves it correctly but it saves it as a new object. I want it to be saved as the one I have selected in my tableView.
You should check out the Core Data Programming Guide. It's hard to know exactly what you want from the question, but the basic idea is:
-(IBAction)saveNote { //hooked up in Interface Builder (or programmatically)
self.currentNote.text = self.textField.text; //assuming currentNote is an NSManagedObject subclass with a property called text, and textField is the UITextField
}
//later, at a convenient time such as application quit
NSError *error = nil;
[self.managedObjectContext save:&error]; //saves the context to disk
EDIT: If you want to edit a preexisting object, you should get the object from the fetched results controller, e.g. NSManagedObject *currentObject = [fetchedResultsController objectAtIndexPath:[self.tableView indexPathForSelectedRow]], then edit that object. I'd also recommend using a custom subclass of NSManagedObject with property declarations, rather than using setValue:forKey, since it's more flexible.
I am trying to create an iPhone application where the user can add entries. When he presses a new entry, a box will popup asking him for some information. Then he can either press "Cancel" or "Save" to discard the data or save it to disk.
For saving, I am using the Core Data framework, which works pretty well. However, I cannot get the "Cancel" button to work. When the window pops up, asking for information, I create a new object in the managed object context (MOC). Then when the user presses cancel, I try to use the NSUndoManager belonging to the MOC.
I would also like to do it using nested undo groups, because there might be nested groups.
To test this, I wrote a simple application. The application is just the "Window based application" template with Core Data enabled. For the Core Data model, I create a single entity called "Entity" with integer attribute "x". Then inside the applicationDidFinishLaunching, I add this code:
- (void)applicationDidFinishLaunching:(UIApplication *)application {
// Override point for customization after app launch
unsigned int x=arc4random()%1000;
[self.managedObjectContext processPendingChanges];
[self.managedObjectContext.undoManager beginUndoGrouping];
NSManagedObject *entity=[NSEntityDescription insertNewObjectForEntityForName:#"Entity"
inManagedObjectContext:self.managedObjectContext];
[entity setValue:[NSNumber numberWithInt:x] forKey:#"x"];
NSLog(#"Insert Value %d",x);
[self.managedObjectContext processPendingChanges];
[self.managedObjectContext.undoManager endUndoGrouping];
[self.managedObjectContext.undoManager undoNestedGroup];
NSFetchRequest *fetchRequest=[[NSFetchRequest alloc] init];
NSEntityDescription *entityEntity=[NSEntityDescription entityForName:#"Entity"
inManagedObjectContext:self.managedObjectContext];
[fetchRequest setEntity:entityEntity];
NSArray *result=[self.managedObjectContext executeFetchRequest:fetchRequest error:nil];
for(entity in result) {
NSLog(#"FETCHED ENTITY %d",[[entity valueForKey:#"x"] intValue]);
}
[window makeKeyAndVisible];
}
The idea is simple. Try to insert a new Entity object, undo it, fetch all Entity objects in the MOC and print them out. If everything worked correctly, there should be no objects at the end.
However, I get this output:
[Session started at 2010-02-20 13:41:49 -0800.]
2010-02-20 13:41:51.695 Untitledundotes[7373:20b] Insert Value 136
2010-02-20 13:41:51.715 Untitledundotes[7373:20b] FETCHED ENTITY 136
As you can see, the object is present in the MOC after I try to undo its creation.
Any suggestions as to what I am doing wrong?
Your problem is caused by the fact that, unlike OS X, the iPhone managed object context does not contain an undo manager by default. You need to explicitly add one.
Change the generated code in the app delegate for the managedObjectContext property to look like this:
- (NSManagedObjectContext *) managedObjectContext {
if (managedObjectContext != nil) {
return managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
managedObjectContext = [[NSManagedObjectContext alloc] init];
//add the following 3 lines of code
NSUndoManager *undoManager = [[NSUndoManager alloc] init];
[managedObjectContext setUndoManager:undoManager];
[undoManager release];
[managedObjectContext setPersistentStoreCoordinator: coordinator];
}
return managedObjectContext;
}
After making that change, the 2nd log message is no longer printed.
Hope that helps...
Dave
I tried Dave approach, but did not work for me.
I finally found the solution in Apple's example CoreDataBooks
The trick is to create a new context that shares the coordinator with you App's context. To discard the changes you dont need to do a thing, just discard the new context object. Since you share the coordinator, saving updates your main context.
Here is my adapted version, where I use a static object for the temp context to create a new ChannelMO object.
//Gets a new ChannelMO that is part of the addingManagedContext
+(ChannelMO*) getNewChannelMO{
// Create a new managed object context for the new channel -- set its persistent store coordinator to the same as that from the fetched results controller's context.
NSManagedObjectContext *addingContext = [[NSManagedObjectContext alloc] init];
addingManagedObjectContext = addingContext;
[addingManagedObjectContext setPersistentStoreCoordinator:[[self getContext] persistentStoreCoordinator]];
ChannelMO* aux = (ChannelMO *)[NSEntityDescription insertNewObjectForEntityForName:#"ChannelMO" inManagedObjectContext:addingManagedObjectContext];
return aux;
}
+(void) saveAddingContext{
NSNotificationCenter *dnc = [NSNotificationCenter defaultCenter];
[dnc addObserver:self selector:#selector(addControllerContextDidSave:)
name:NSManagedObjectContextDidSaveNotification object:addingManagedObjectContext];
NSError *error;
if (![addingManagedObjectContext save:&error]) {
// Update to handle the error appropriately.
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
exit(-1); // Fail
}
[dnc removeObserver:self name:NSManagedObjectContextDidSaveNotification object:addingManagedObjectContext];
// Release the adding managed object context.
addingManagedObjectContext = nil;
}
I hope it helps
Gonso
It should work. Did you correctly assign the undo manager to your managedObjectContext? If you have rightly done that, it by default has undo registration enabled, and you should be good to go. There is a good article on core data here. There is a good tutorial on core data and NSUndoManager here. Hope that helps.