Making Core Data Model Class Accessible (App design) - ios

Question

Started down the path of 'singleton'. (whew!!) Now, trying to retrace some steps AND take the core data stack OUT of the app delegate.
In a discussion of this, I saw the following code:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions(NSDictionary *)launchOptions {
DataModel *dataModel = [[DataModel alloc] init];
self.rootViewController.dataModel = dataModel;
...
}
In DataModel.m is the core data stack, methods to initiate a web service and methods to save the returned data into core data. Connection is another class.
Launch, starting the connection, passing the managed object context to the root view controller and receiving the web data all work fine. Then, a posted notification (upon completion of data receipt) in Connection class notifies DataModel of data to process. The issue is DataModel has been deallocated. The app crashes.
After abandoning the (shhh) singleton class for DataModel, the question(s) then are: How can the DataModel be kept around to process the received web data, destined for core data? Or, would it be better to split the core data stack and processing the received data into 2 files?
It seems logical to have the core data stack and processing methods in one class. I want to build this app by passing the context from controller to controller.

Answer 1

I have a class, "SVODataHelper" that has this in it:
#pragma mark - Setup
- (id) init
{
self = [super init];
if (!self)
return nil;
_model = [NSManagedObjectModel mergedModelFromBundles:nil];
_coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:_model];
_context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_context setPersistentStoreCoordinator:_coordinator];
return self;
}
- (void) loadStore
{
if (_store)
return;
NSError *error = nil;
_store = [_coordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:[self storeURL] options:nil error:&error];
if (!_store)
{
NSLog(#"Failed to add store. Error: %#", error);
abort();
}
}
- (void) setupCoreData
{
[self loadStore];
}
Then, in AppDelegate, I use:
- (SVOData *)svoData
{
if (!_svoDataHelper)
{
static dispatch_once_t predicate;
dispatch_once (&predicate, ^{ _svoDataHelper = [[SVOData alloc] init]; }); // insures a single instance created to guarantee thread safety.
[_svoDataHelper setupCoreData];
}
return _svoDataHelper;
}
And finally, I access the helper class with:
svoDataHelper = [(AppDelegate *)[[UIApplication sharedApplication] delegate] svoData];
I don't know if it is good or bad but it works. I got the concept from some book I read ("Learning IOS Core Data?) and it looked pretty clean as it allowed me to keep the essential stuff in a separate class while avoiding having to pass a pointer to that class around.