What's the best way to reverse communicate between view controllers?

Question

I've been thinking about this and have read through another stackoverflow question regarding the best recommended way to communicate between view controllers. However, the question/answer for that doesn't seem to address the best approach for the reverse behavior.

i.e. to pass data from ParentController to its ModalController, we could initialize ModalController like initWithDataToProcess:.

But what if we want to do the reverse? How would I notify the previous controller about a new data?

e.g. User clicks on 'new person' button on the ParentController. I initiate a new ModalController and present the user with a person editor view via presentModalViewController:. User clicks on 'done' to add a new person. I dismissModalViewController: and UI returns to the ParentController's view.

Using a global field reference in a singleton object (app delegate or other) is bad. delegation (via formal protocol) and notifications (via NSNotificationCenter) seems overkill. Any suggestions?

Answer 1

A delegate is pretty much the minimum you can do. If you think it is too much of a hassle to declare a new protocol for this, just pass in the parent view controller and have the modal one call a method on it.

Answer 2

It is generally cleaner to use notifications. Just add your observer like this....

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(somethingHappened:) name:@"MyNotification" object:nil];

and elsewhere in your code you'd post the notification whenever you need to.

[[NSNotificationCenter defaultCenter] postNotificationName:@"MyNotification" object:self];

In the example I'm passing self but you can pass any object you wish really and it will be fed to your somethingHappened: function

The important thing is to keep the @"MyNotification" very descriptive and unique. Adding your project name to the beginning is a good way to keep things unique...eg. @"ProjAXViewHasGotData"