Key data: UIManagedDocument or AppDelegate to set the main data stack?

UIManagedDocument ( ) iCloud. .

AppDelegate, , . , Core Data, Xcode.

ManagedObjectContext viewController. , . , MOC viewcontroller, .

singleton DataAccessLayer:

DataAccessLayer.h

@interface DataAccessLayer : NSObject

   //Saves the Data Model onto the DB
   - (void)saveContext;

   //DataAccessLayer singleton instance shared across application
   + (id) sharedInstance;
   + (void)disposeInstance;
   // Returns the managed object context for the application.
   // If the context doesn't already exist, it is created and bound 
   // to the persistent store coordinator for the application.
   + (NSManagedObjectContext *)context;
@end

DataAccessLayer.m

#import "DataAccessLayer.h"

//static instance for singleton implementation
static DataAccessLayer __strong *manager = nil;

//Private instance methods/properties
@interface DataAccessLayer ()

// Returns the managed object context for the application.
// If the context doesn't already exist, it is created and 
// bound to the persistent store coordinator for the application.
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the application model.
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;

// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the application 
// store added to it.
@property (readonly,strong,nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;

// Returns the URL to the application Documents directory.
- (NSURL *)applicationDocumentsDirectory;
@end


@implementation DataAccessLayer

@synthesize managedObjectContext = __managedObjectContext;
@synthesize managedObjectModel = __managedObjectModel;
@synthesize persistentStoreCoordinator = __persistentStoreCoordinator;

//DataAccessLayer singleton instance shared across application
+ (id)sharedInstance
{
    @synchronized(self) 
    {
        if (manager == nil)
            manager = [[self alloc] init];
    }
    return manager;
}

+ (void)disposeInstance
{
    @synchronized(self)
    {
        manager = nil;
    }
}

+(NSManagedObjectContext *)context
{
    return [[DataAccessLayer sharedInstance] managedObjectContext];
}

//Saves the Data Model onto the DB
- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil) 
    {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) 
        {
            //Need to come up with a better error management here.
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        } 
    }
}

// Returns the managed object context for the application.
// If the context doesn't already exist, it is created and 
// bound to the persistent store coordinator for the application.
- (NSManagedObjectContext *)managedObjectContext
{
    if (__managedObjectContext != nil)
        return __managedObjectContext;

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) 
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init];
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return __managedObjectContext;
}

// Returns the managed object model for the application.
// If the model doesn't already exist, it is created from the 
// application model.
- (NSManagedObjectModel *)managedObjectModel
{
    if (__managedObjectModel != nil) 
        return __managedObjectModel;

    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Model" 
                                               withExtension:@"momd"];
    __managedObjectModel = [[NSManagedObjectModel alloc] 
                         initWithContentsOfURL:modelURL];
    return __managedObjectModel;
}

// Returns the persistent store coordinator for the application.
// If the coordinator doesn't already exist, it is created and the 
// application store added to it.
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil) 
        return __persistentStoreCoordinator;

    NSURL *storeURL = [[self applicationDocumentsDirectory] 
                         URLByAppendingPathComponent:@"MyData.sqlite"];

    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]
                                     initWithManagedObjectModel:[self managedObjectModel]];

    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
                           configuration:nil URL:storeURL options:nil error:&error]) 
    {
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}

// Returns the URL to the application Documents directory.
- (NSURL *)applicationDocumentsDirectory
{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory
                                         inDomains:NSUserDomainMask] lastObject];
}

@end

, , , :

NSManagedObjectContext *context = [DataAccessLayer context];

, , . NSManagedObjectContext - , , . , Core Data , . Apple:

, . NSOperation, , init , . initues queues, . ( ) ( ).

, . "" , :

• (objectID) objectWithID: existingObjectWithID: error: . - .
• .