Category + app delegate method for handling Core Data objects in UIKit state restoration. There's a bit of a chicken-and-egg problem in state restoration—you can't store the managed object context in the restorable state, but you can't restore without it. The usual, horrible, solution is to make the state restoration code retrieve the context fr…

MyRestorableAppDelegate.m

@implementation MyRestorableAppDelegate

...

- (UIViewController *)application:(UIApplication *)application viewControllerWithRestorationIdentifierPath:(NSArray *)identifierComponents coder:(NSCoder *)coder {
    coder.managedObjectContext = self.managedObjectContext;
    return nil;
}

...

@end

NSCoder+managedObjectContext.h

//
//  NSCoder+managedObjectContext.h
//  Feeder
//
//  Created by Brent Royal-Gordon on 7/2/13.
//  Copyright (c) 2013 Architechies. All rights reserved.
//

#import <Foundation/Foundation.h>

@interface NSCoder (managedObjectContext)

@property (nonatomic, strong) NSManagedObjectContext * managedObjectContext;

- (void)encodeManagedObject:(NSManagedObject*)managedObject forKey:(NSString*)key;
- (id)decodeManagedObjectOfEntityNamed:(NSString*)entityName forKey:(NSString*)key;

@end

NSCoder+managedObjectContext.m

//
//  NSCoder+managedObjectContext.m
//  Feeder
//
//  Created by Brent Royal-Gordon on 7/2/13.
//  Copyright (c) 2013 Architechies. All rights reserved.
//

#import "NSCoder+managedObjectContext.h"
#import <objc/runtime.h>

@implementation NSCoder (managedObjectContext)

- (NSManagedObjectContext *)managedObjectContext {
    return objc_getAssociatedObject(self, _cmd);
}

- (void)setManagedObjectContext:(NSManagedObjectContext *)managedObjectContext {
    objc_setAssociatedObject(self, @selector(managedObjectContext), managedObjectContext, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
}

- (void)encodeManagedObject:(NSManagedObject *)managedObject forKey:(NSString *)key {
    [self encodeObject:managedObject.objectID.URIRepresentation forKey:key];
}

- (id)decodeManagedObjectOfEntityNamed:(NSString*)entityName forKey:(NSString*)key {
    NSURL * objectURL = [self decodeObjectOfClass:NSURL.class forKey:key];
    NSManagedObjectID * objectID = [self.managedObjectContext.persistentStoreCoordinator managedObjectIDForURIRepresentation:objectURL];
    
    NSFetchRequest * req = [NSFetchRequest fetchRequestWithEntityName:entityName];
    req.predicate = [NSPredicate predicateWithFormat:@"self == %@", objectID];
    
    return [self.managedObjectContext executeFetchRequest:req error:NULL].firstObject;
}

@end