Actually what I tend to do is grab the context from the tabBarController of the view you are in. For instance, in your viewWillAppear from the view in the tab bar just create an instance of self.tabBarController and set your views context to that context. That way you can just pass the context to the tabBar and each view can reference that tabBar's context.
Something like this.
MainTabBar *parentTabBarController = (MyTabBar *)self.tabBarController;
self.managedObjectContext = parentTabBarController.managedObjectContext;