Question

Just curious why ManagedObjectContexts should be passed to UIViewControllers when they are created, rather than just grabbing them from a UIApplicationDelegate?

The docs say that this makes your applications more rigid, but I am failing to see the nuances of when to use which pattern.

Thanks!

Answer 1

Imagine that I ask you to do some task, like painting a room. If I just tell you “go paint a room,” you’ll need to ask me a lot of questions, like:

• Which room?
• Where’s the paint?
• Where are the brushes?
• Should I use a dropcloth?

In short, you won’t be able to complete the task without help from me. If you have to depend on me every time, you won’t be a very flexible painter. One way to deal with that problem is for me to give you all the stuff you need at the outset. Instead of “go paint a room,” I’ll say “please paint room number 348 using this bucket of paint and this brush, and don’t bother with a dropcloth.” Now, you’ve got everything you need, and you can get right to work with no further help from me. You’re a much more flexible worker because you no longer depend on me.

The same thing applies to view controllers (and objects generally); it’s better to give them everything they need than to have them depend on a particular object like the app delegate. It’s true not just for managed object contexts, but for any information they need to do their job.