Saving and loading data when application enters / leaves background

Question

I am attempting to make my game persist its current state and reload it when a user exits or restarts the game. What I am struggling with, however, is how to actually get access to the objects at the right time. Here is the pseudo code for what I need, I just cant seem to get access to the right objects, am I doing this backwards or is this the correct way to do it?

So to reiterate, my problem here is getting access to the correct ViewControllers in order to save / load the data from disk.

My Navigation hierarchy is simple, ViewController > GameViewController (shown modally)

-(void)applicationDidEnterBackground:(UIApplication *)application
{
  // Save current state to disk

  // See if GameViewController (or GameView) is top controller (aka game in progress)
  // If so then use NSKeyedArchiver to persist to disk
}

-(void)applicationDidBecomeActive:(UIApplication *)application
{
  // Load current state from disk

  // Use NSKeyedArchiver to load data from disk, if game is in progress then
  // Find mainViewController, then show the game modal on top of it
  // then populate the game data with the data from disk
}

Bonus question: Are these two functions the correct ones to be doing my saving / loading in?

Answer 1

lternatively you could set up a notification handler wherever you want/need in your code:

[[NSNotificationCenter defaultCenter] addObserver: self
                                         selector: @selector(handleEnteredBackground:) 
                                             name: UIApplicationDidEnterBackgroundNotification
                                           object: nil];

Answer 2

The correct way to solve this is to make use of the Model-View-Controller pattern (MVC) - as (almost) all good Cocoa iOS apps should:

• First, ensure any data that you want to persist is stored in your model layer/object(s).
• If the view controller's states change frequently, use the notification: UIApplicationWillEnterBackgroundNotification in the view controllers as the trigger to save the state to the model.
• When the applicationDidEnterBackground: message is received in the app delegate, save the data in the model objects to the file system.
• When the application wakes up or is restarted, load the file data back into the model and notify the view controllers via a custom notification so the view controllers know to restore their relevant states.

The app delegate shouldn't go around picking out bits of information from each view controller that it wants to save to the file system.