Master-Detail-View manageObject is not set correct - ios

Question

I try to get an Master-Detail-View with CollectionView instead of TableView up and running. Basicly I followed the examples of http://goo.gl/e07Bs and http://goo.gl/tGLVY to get it working. As with Xcide 4.6 the boilerplate changed a little bit, but I tried my best.
When I run a smoke-test the app crashes with the Message:
1 -fetchedResultsController value self.mOContext 0x00000000
2013-02-12 20:33:52.895 foobar[1461:c07] *** Terminating app
due to uncaught exception 'NSInvalidArgumentException', reason:
'+entityForName: nil is not a legal NSManagedObjectContext
parameter searching for entity name 'PhotoModel''
The error seems to be in this line:
NSEntityDescription *entity = [NSEntityDescription entityForName:#"PhotoModel" inManagedObjectContext:self.managedObjectContext];
I created a breakpoint before this line and checked the content of managedObjectContext, as seen above in the log it is empty (first line, self.mOContext).
How do I set the managedObjectContext, or where is my error that this is not working...?
Edit: As I needed a new scene before the master-detail-scenes, i had to change the AppDelegate.m to meet the new requirements. I'd comment the intial boilerplate of didFinishLaunchingWithOptions to get the initial scene working:
#import "AppDelegate.h"
#import "MasterViewController.h"
#import "LoginViewController.h"
#implementation AppDelegate
#synthesize managedObjectContext = _managedObjectContext;
#synthesize managedObjectModel = _managedObjectModel;
#synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
// Override point for customization after application launch.
/*
// Old Master-Detail-View-Controller, commented to get the initial new scene to work
UINavigationController *navigationController = (UINavigationController *)self.window.rootViewController;
MasterViewController *controller = (MasterViewController *)navigationController.topViewController;
controller.managedObjectContext = self.managedObjectContext;
*/
return YES;
}
Heres my MasterViewController.h
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
#interface MasterViewController : UICollectionViewController <NSFetchedResultsControllerDelegate>
#property (strong, nonatomic) NSFetchedResultsController *fetchedResultsController;
#property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;
#end
and MasterViewController.m
#import "MasterViewController.h"
#import "CollectionViewCell.h"
#import "DetailViewController.h"
static NSString *cellid = #"cellid";
#interface MasterViewController ()
- (void)configureCell:(UICollectionViewCell *)cell atIndexPath:(NSIndexPath *)indexPath;
#end
#implementation MasterViewController
{
NSMutableArray *_objectChanges;
NSMutableArray *_sectionChanges;
}
- (void)awakeFromNib
{
[super awakeFromNib];
}
- (void)viewDidLoad
{
[super viewDidLoad];
// Do any additional setup after loading the view, typically from a nib.
// not sure if needed
self.navigationItem.leftBarButtonItem = self.editButtonItem;
UIBarButtonItem *addButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemAdd target:self action:#selector(insertNewObject:)];
self.navigationItem.rightBarButtonItem = addButton;
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
- (void)insertNewObject:(id)sender
{
NSManagedObjectContext *context = [self.fetchedResultsController managedObjectContext];
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.
NSError *error = nil;
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.
NSLog(#"Unresolved error %#, %#", error, [error userInfo]);
abort();
}
}
#pragma mark - Collection View
- (NSInteger)numberOfSectionsInCollectionView:(UICollectionView *)collectionView
{
return [[self.fetchedResultsController sections] count];
}
- (NSInteger)collectionView:(UICollectionView *)collectionView numberOfItemsInSection:(NSInteger)section
{
id <NSFetchedResultsSectionInfo> sectionInfo = [self.fetchedResultsController sections][section];
return [sectionInfo numberOfObjects];
}
- (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath
{
CollectionViewCell *cell = (CollectionViewCell *)[collectionView dequeueReusableCellWithReuseIdentifier:cellid forIndexPath:indexPath];
NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
#warning Unimplementd Cell Configuration
return cell;
}
#pragma mark - Segue
- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender
{
if ([[segue identifier] isEqualToString:#"showDetail"]) {
NSIndexPath *indexPath = [[self.collectionView indexPathsForSelectedItems] lastObject];
NSManagedObject *object = [[self fetchedResultsController] objectAtIndexPath:indexPath];
[[segue destinationViewController] setDetailItem:object];
}
}
#pragma mark - Fetched results controller
- (NSFetchedResultsController *)fetchedResultsController
{
if (_fetchedResultsController != nil) {
return _fetchedResultsController;
}
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
// Edit the entity name as appropriate.
NSEntityDescription *entity = [NSEntityDescription entityForName:#"PhotoModel" 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:#"timeStamp" ascending:NO];
NSArray *sortDescriptors = #[sortDescriptor];
[fetchRequest setSortDescriptors:sortDescriptors];
// 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:#"Master"];
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;
}
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
NSMutableDictionary *change = [NSMutableDictionary new];
switch(type) {
case NSFetchedResultsChangeInsert:
change[#(type)] = #(sectionIndex);
break;
case NSFetchedResultsChangeDelete:
change[#(type)] = #(sectionIndex);
break;
}
[_sectionChanges addObject:change];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
newIndexPath:(NSIndexPath *)newIndexPath
{
UICollectionView *collectionView = self.collectionView;
NSMutableDictionary *change = [NSMutableDictionary new];
switch(type) {
case NSFetchedResultsChangeInsert:
change[#(type)] = newIndexPath;
break;
case NSFetchedResultsChangeDelete:
change[#(type)] = newIndexPath;
break;
case NSFetchedResultsChangeUpdate:
change[#(type)] = newIndexPath;
break;
case NSFetchedResultsChangeMove:
change[#(type)] = #[indexPath, newIndexPath];
break;
}
[_objectChanges addObject:change];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
if ([_sectionChanges count] > 0)
{
[self.collectionView performBatchUpdates:^{
for (NSDictionary *change in _sectionChanges)
{
[change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) {
NSFetchedResultsChangeType type = [key unsignedIntegerValue];
switch (type)
{
case NSFetchedResultsChangeInsert:
[self.collectionView insertSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]]];
break;
case NSFetchedResultsChangeDelete:
[self.collectionView deleteSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]]];
break;
case NSFetchedResultsChangeUpdate:
[self.collectionView reloadSections:[NSIndexSet indexSetWithIndex:[obj unsignedIntegerValue]]];
break;
}
}];
}
} completion:nil];
}
if ([_objectChanges count] > 0 && [_sectionChanges count] == 0)
{
[self.collectionView performBatchUpdates:^{
for (NSDictionary *change in _objectChanges)
{
[change enumerateKeysAndObjectsUsingBlock:^(NSNumber *key, id obj, BOOL *stop) {
NSFetchedResultsChangeType type = [key unsignedIntegerValue];
switch (type)
{
case NSFetchedResultsChangeInsert:
[self.collectionView insertItemsAtIndexPaths:#[obj]];
break;
case NSFetchedResultsChangeDelete:
[self.collectionView deleteItemsAtIndexPaths:#[obj]];
break;
case NSFetchedResultsChangeUpdate:
[self.collectionView reloadItemsAtIndexPaths:#[obj]];
break;
case NSFetchedResultsChangeMove:
[self.collectionView moveItemAtIndexPath:obj[0] toIndexPath:obj[1]];
break;
}
}];
}
} completion:nil];
}
[_sectionChanges removeAllObjects];
[_objectChanges removeAllObjects];
}
- (void)configureCell:(UICollectionViewCell *)cell atIndexPath:(NSIndexPath *)indexPath
{
NSManagedObject *object = [self.fetchedResultsController objectAtIndexPath:indexPath];
//cell.textLabel.text = [[object valueForKey:#"timeStamp"] description];
#warning textlabel has to be created in storyboard
}
#end

Answer 1

The managedObjectContext is usually created in the boilerplate code by XCode. When you create the project, make sure to enable Core Data. During the project creation wizard, there should be a checkbox to "Use Core Data". This will insert the correct boilerplate code to create the managed object context and the persistantstorecoordinator, both of which you will need whenever working with Core Data.
EDIT:
In the old AppDelegate code that you commented out, they set the managedObjectContext variable in the master view controller to self.managedObjectContext here:
controller.managedObjectContext = self.managedObjectContext;
Did you make sure to do the same thing for your custom controller?