Managedobject在UIViewController中变为nil

Question

当我尝试在视图控制器中加载其属性时，Managedobject变为零。我的操作流程如下。我的所有操作都发生在主线程（thread1）中。

1. 我在MOC1中保存了一个新实体。
2. 然后我在MOC2中获取这个新创建的实体（我已经订阅了NSManagedObjectContextDidSaveNotification，并且在MOC1中完成的更改被合并到MOC2）。
3. 然后将检索到的Managed Object设置为singleton class的属性。
4. 之后我加载一个视图控制器。
5. 当我尝试从singleton类获取managedobject的属性时，内部视图控制器，我得到nil。

这里我从moc2

创建一个managedobject

ManagedObjectClass* someClass = (ManagedObjectClass*)[NSEntityDescription insertNewObjectForEntityForName:@"ManagedObjectClass" inManagedObjectContext:moc2];

    someClass.orderID = @"123";
    NSError *error = nil;
    moc2 save:&error];

//下面是我的NSManagedObjectContextDidSaveNotification处理程序

- (void) mocDidSaveNotification:(NSNotification *)notification
{
    NSManagedObjectContext *savedContext = [notification object];

    // ignore change notifications for the main MOC
    if ([CoreDataController sharedCoreDataController].moc2 == savedContext)
    {
        return;
    }

    dispatch_async(dispatch_get_main_queue(), ^{
        [[CoreDataController sharedCoreDataController].moc1 mergeChangesFromContextDidSaveNotification:notification];
    });
}

//现在使用moc1

获取创建的someClass

dispatch_async(dispatch_get_main_queue(),^{

    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc]init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"ManagedObjectClass" inManagedObjectContext:moc1];
    [fetchRequest setEntity:entity];

    NSPredicate *matchedPredicate = [NSPredicate predicateWithFormat:@"orderID = 123"];
    [fetchRequest setPredicate:matchedPredicate];

    NSError *error = nil;
    NSMutableArray *fetchedObjects = [[[moc1 executeFetchRequest:fetchRequest error:&error]mutableCopy]autorelease];

    // Here am able to see the contents of currentOrder
    [appcontroller sharedAppController].currentOrder = [fetchedObjects objectAtIndex:0]

});

//现在加载视图控制器

DetailsViewController *aSelectedViewController = [[DetailsViewController alloc]initWithNibName:@"DetailsViewController" bundle:nil];
UINavigationController aNavigationController = [[[UINavigationController alloc] initWithRootViewController:aSelectedViewController]autorelease];
self.applicationWindow.rootViewController = navigationController;

//查看控制器的实现

@implementation DetailsViewController

- (void)viewDidLoad
{
    if([appcontroller sharedAppController].currentOrder == nil)
    {
        NSLog(@"currentOrder became nil");
    }
}
@end