Pass data from any view controller to one master view controller in iOS

Question

I am building a music player app -- in this app, the music player view controller will always sit on top of any other sub-viewcontroller (navigation view, table views, etc) I need actions taken in any potential subview to be sent back up to the player view controller (for example, user selects "play" on a profile page, and I send that event back up) My question is what is the best way to do this? I apologize in advance for being a bit nebulous, but I already know of three ways I can implement it. I just want to know what the "right" way is.

These are the three ways I've thought of:

1.Delegate pattern -- pass the Music Player Controller off to it's children controllers and set itself as the delegate for whenever that event is passed (messy because the first view controller is a navigation view controller, so I think I'd have to pass it down several levels meaning several delegates (correct me if I'm wrong))

2.Notification Center -- register the player view controller for a particular notification, encapsulate the data that's sent from the other viewcontrollers so that I can perform my actions.

3.Singleton-like access of the player view controller - basically allow access to the player view controller from any view controller.

Any help is appreciate to steer me in the right direction. I can do it either of these ways, but as this is a "learning" app, would love to do it right.

Answer 1

IMHO there is no "right way". Frankly I was thinking of all three of them when I read the subject line only.

As you are asing for opinions... I would not recommend the singleton pattern here. This is just because view controllers could stack and by their nature be instanciated multiple times. In terms of maintainable code (readability by others) I'd say no to that approach.

The delegate pattern is fine. But as you say you would have to pass a reference to this view controller from one view controller to the next. Yes, a bit messy. Well, you could store a reference to the delegate in some singleton. That is not the same as designing a view controller as singleton.

I'd say that the notification center is most appropriate for this type of data flow. Sender and receiver of the message are totally detatched and don't need to 'know each other'. It is a perfect pattern for all kinds of multiple senders and/or mulitple receipient type of messages.

Well, as I said, this is just an opinion.

Answer 2

I would not recommend broadcast notifications (via NSNotificationCenter), they are hard to debug, other developers will have problems to understand, whats going on in your application (application flow), every developer must maintain a global list with all notification names (notificationSender and observer must use the same notification name and they are usually constant string variables), observer can not send back any data after receiving a notification, etc. Broadcasting is really helpful, if all controllers should be notified of the same event (for example Login/Logout events).

If possible, i think one should allways try to use a Delegate Pattern (with clearly defined protocol). Maybe something like:

id <SubViewControllerEvents>musicPlayerVC= [MyMusicAppManager delegate];
if ( [musicPlayerVC respondsToSelector:@selector(userDidSelectPlay)] ) {
   [musicPlayerVC userDidSelectPlay];
}