Where should I store data/state information as I switch ViewControllers?

Question

Hi,

I am just starting to develop on the iPhone and was wondering about storing data that the user is entering into my application.

Question: My application is organized as:

• UITabController
  • LoginViewController (UIViewController)
  • UINavigationController
  • • CustomViewController1 (UIViewController)
  • • CustomViewController2 (UIViewController)
  • • CustomViewController3 (UIViewController)
  • UINavigationController
  • • CustomerViewController3 (this has a UITableView that allows the user to go to a Detail View and then a Map View)

How should I be storing the input from the user?

1. When the user logs in, I need to cache their username and password, so that I can pass it to web services.
2. Also, I have an option to allow the user to save their username and password. Where should I store this information?
3. In CustomViewController1,2,3, I collect various input and then at some point, pass it to a web service. I need to store this and the response of the web service, so that if the user wants to cancel I have the necessary IDs to send to the "cancel" web service.
4. How do I create a "global variable" that can be stored and then any view controller can see?

Any information and code examples would be hugely appreciated to getting me long the way.

I have most of the Apple iOS Programming Guide and it's supporting PDFs printed out, but those can be really intimidating to someone new on the platform just trying to get started.

Thanks again! Jason

Answer 1

Your first pass at all this could be accomplished very simply by using the NSUserDefaults class (code samples in the docs). It's a place to persistently store simple information, and access it from anywhere in your app. As you learn more of the API and figure out more specific needs, you can branch out and use local file system storage, Core Data, etc.

Answer 2

If you're not looking for a way to store data related to the current user, but just have data accessible by all viewcontrollers, there are two ways.

a) recommended: create a singleton class, and import this class into the viewcontrollers b) declare objects in the app delegate, and access them with [[UIApplication SharedApplication] delegate].objectname.

I must confess that I use b) for now blush. This will cover your points 1,2,4, I think. For point 3, see jbm's recommendation - or write them to a file in the app's sandbox, which I don't recommend for passwords.