Explore the Game Application Life Cycle - Beginning iOS6 Games Development - page 59

special tasks, because an int is not an object. NSCoder provides a special task for primitive types. In
our case, we use decodeInt:ForKey: and encodeInt:ForKey: . There exists analog task for the other
primitive types, like BOOL , float , double , and so on.
We have looked at the implementation required by a class we wish to archive (and unarchive), but
we have not looked at how we actually unarchive an object from the user's preferences. Listing 3-16
shows how this is done in the class HighscoreController .
Listing 3-16. HighscoreController (viewDidLoad)
- (void)viewDidLoad
{
[super viewDidLoad];
[highscores release];
NSData* highscoresData = [[NSUserDefaults standardUserDefaults] dataForKey:KEY_HIGHSCORES];
if (highscoresData == nil){
highscores = [[[Highscores alloc] initWithDefaults] retain];
[self saveHighscores];
} else {
highscores = [[NSKeyedUnarchiver unarchiveObjectWithData: highscoresData] retain];
}
[self layoutScores:nil];
}
The viewDidLoad task from Listing 3-16 is called when a HighscoreController 's view is loaded. In
this task, we want to prepare the HighscoreController for use. This means making sure highscores
is in a usable and accurate state, and we want to lay out the current set of high scores in case this
view is displayed before a new Score is added. In order to retrieve the current high scores, we read
a NSData object from the NSUserDefaults object returned by the call to standardUserDefaults . If
the NSData object is nil , which will happen the first time you run the application, we initialize a new
Highscores object and immediately save it. If the NSData object is not nil , we unarchive it with a call
to NSKeyedUnarchiver 's task unarchiveObjectWithData and retain the results.
We have looked at how an object can be archived and unarchived in this section. We will now use
the same principles to show how we can archive and unarchive our game state.
Preserving Game State
With the advent of background execution on iOS devices, the importance of preserving game or
application state is a bit reduced. But a fully functional and user-friendly application should be able
to gracefully handle restoring state if the application is terminated. The steps required to preserve
state are really not that different from storing other types of data. This is a critical feature of many
applications.
The first thing we need to understand is when we should be trying to restore state or archive state.
Figure 3-11 is a flowchart describing our sample application's life cycle in terms of initialization.