I am building a remote app which is receiving different states of its accessory. It is receiving things like: power state on/off, volume state 5, equalizer setting jazz, etc. and has nothing more to do than map theses states into the UI with selected or unselected states and send changes done back to the accessory.
About the app architecture:
The app is connected with it's accessory as illustrated in Apples EADemo project using the external accessory framework.
The UI is build within non-repeating customized UITableViewCell full of UIButtons. When starting the app a data model class will receive all current states from the examples EADSessionController and has to communicate theses states to the UI (the cells directly rather than the UITableViewController) with one of the mentioned patterns. This will be a stand alone, one-page app looking like a real remote.
Thinking of NSNotification, delegates and KVO (key-value-observing) I am trying to figure out which of these patterns I should use for this special approach?
Any answer on why choosing one of them and a brief description on how to implement would be appreciated. If your answer will be KVO please give some more insights since I never used this pattern so far.
It really depends.
The most loosely coupled one is to use NSNotification and NSNotificationCenter, as the instance which post the notification does not necessarily have knowledge about the observer, and there can be more than one observer.
The delegate pattern is a little more rigid, and there could usually be only one delegate object that receives a message. If the UITableViewController in your project is the only instance that handles a message(, or it would properly propagate the message to other components), it is still OK.
The KVO pattern requires more precisely designed observation relationship. You will have and have to look after exactly how the KVO is implemented. And KVO also allows one-to-many observation. The down side of KVO is if the observing relationship is dynamic and transient, you must take much more care about how these objects were torn down, or you could get a lot of crashes like sending updates to a dealloc'ed instance, etc.
If you are working on a library which would be delivered to a 3rd party to use, perhaps NSNotification would be the first choice.