iOS: Core Data class method - objective-c

Question

Is it possible and practical to create a Core Data class method that will return the current instance of managedObjectContext? I am wondering so that I can segue to other controllers and load modal views without having to pass the managedObjectContext.
Also if I am using Core Data with dispatch_async I know I need to create my own instance of managedObjectContext but I can use the same coordinator. Will this make the information accessible both inside the dispatch_async and in the main thread?
I am basically using the dispatch_async to get data from the API and store it while the user is using the application.

Answer 1

In the past, I've created a Core Data manager singleton class that has simplified things. Here is an example, but this is pre-iOS5/ARC, so some changes need to be made.

Answer 2

I had a similar issue when trying to asynchronously getting data from my server to the app. My method is a bit different, but basically here it is (this is a 4.3 project, so no ARC):
The following methods are in my DataUpdater singleton. This first method is called at app startup:
- (void) update { //download the updates on a new thread
[NSThread detachNewThreadSelector:#selector(updateThread)
toTarget:self withObject:nil];
}
It initializes a thread with this selector, which is responsible only for downloading the content from the API, then passing it back to the main thread to be saved.
- (void) updateThread { //the actual update thread
//New thread, new auto-release pool
//(dunno if you need to do anything fancy for ARC)
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
//...
//YOUR CODE TO DOWNLOAD (BUT *NOT* SAVE) DATA FROM THE SERVER
//DON'T CREATE ANY MANAGED OBJECTS HERE
//...
//Pass the data to the main thread to perform
//the commit to the Core Data Model
[self performSelectorOnMainThread:#selector(saveUpdate:)
withObject:data waitUntilDone:NO];
//kill the thread & the auto-release pool
[NSThread exit];
[pool release];
}
Now that we're back on the main thread, the data is added to the Core Data Model and then the context is saved.
- (void) saveUpdate:(NSArray *) data {
//add the objects to your Core Data Model
//and save context
NSError * error = nil;
[[[CoreManager defaultCoreManager] CoreContext] save:&error];
if (error) {
[NSException raise:#"Unable to save data update"
format:#"Reason: %#", [error localizedDescription]];
} else {
[[NSNotificationCenter defaultCenter] postNotification:
[NSNotification notificationWithName:#"DONE" object:nil]];
}
}

Answer 3

Dealing with the first part of the question only (you shouldnt really ask multiple questions!) you don't have to pass the managed object context around - presumably you are passing a managed object? In that case the context is available as a property of the managed object itself - .managedObjectContext.