Cocoa touch connection and data design pattern

Question

My question is a design issue and it has been driving crazy over the last couple of days. I am new to cocoa touch development.

I have an application that has a UINavigarion controller and a 3 views. I need to keep communicate with a WCF service and store the data on the app side.

How do I create my Model (MVC) in a way that makes the data available to all controllers?

What I started doing is a singleton that handles all the storage and web calls but I read thru the threads that it is a bad idea. I also considered putting the code in the appDelegate but people say that is a bad idea too.

Conceptually how would u design your model and communicate with the controllers?

Any help is much appreciated.

Answer 1

You will get different advice because opinions differ on the best method to use. As you noted, for handling a data model, there are two major design patterns: Dependency Injection and Singleton.

Dependency Injection relies on passing the data model object from view controller to view controller as needed. Marcus Zarra (author of Core Data: Apple's API for Persisting Data on Mac OS X which I recommend) wrote a good article explaining Dependency Injection. Most of the Apple documentation recommends that you use the Dependency Injection design.

I like the Singleton pattern but it is very, very, very dangerous for a novice to use. The Singleton pattern is so easy to do wrong that most graybeards have given up on it and simply advise novices to never use it.

The Singleton pattern has the advantage of increasing modularity and flexibility of the app. However, it requires that you have a firm idea of what the data model will do before you start coding both the Data Model and the UI. It requires more work up front to get correct and it is not as forgiving as Dependency Injection. You have to use singletons with greater discipline.

For a simple app with three hierarchal views, Dependency Injection is the simplest and cleanest design to implement. You won't need the flexibility of a singleton and a singleton will just add unneeded complexity. The Navigation-based template with Core Data provided by Xcode will give you 50% of the app to start. Just add the second and third tier views and you're done.