I'm really scratchng my head trying to work out where my managed object context is vanishing to.
I'm originally instantiating it within my app delegate and then passing it into a retained property within an NSWindowController as such:
self.TPWC = [[TestPanelWindowController alloc] initWithWindowNibName:@"TestPanel"];
self.TPWC.managedObjectContext = self.managedObjectContext;
self.TPWC.persistentStoreCoordinator = self.persistentStoreCoordinator;
[TPWC.window makeKeyAndOrderFront:nil];
I've then got a button that should instantiate an NSManagedObject and insert it into the managed object context like this:
NSManagedObject *newInstanceOfSomeEntity =
[NSEntityDescription insertNewObjectForEntityForName:@"SomeEntity"
inManagedObjectContext:self.managedObjectContext];
At this point, self.managedObjectContext has somehow become nil.
I've inserted a breakpoint into windowDidLoad and I can confirm that at that point, we do have a valid instance of an NSManagedObjectContext, but it's somehow become nil in between viewDidLoad and then trying to insert a managed object.
I've tried creating a custom initialiser to set the NSManagedObjectContext but it's still becoming nil.
Core Data is quite new to me and I'm struggling to understand what's going wrong.
This is not a direct answer to why you're seeing your context disappear, but it could still fix your problem:
From an architecture standpoint, you really shouldn't be passing around the managed object context between objects, especially UI objects.
Instead you should have a global singleton class that instantiates the managed object context (along with the coordinator and persistent store, probably), and then provide access to it via a public property. Then, from your window controller, you would just access it from the singleton object.
(A side note if you're using multi-threading, be careful of accessing and using the same context from different threads.)