Explore the Game Application Life Cycle - Beginning iOS6 Games Development - page 57

- (id)initWithCoder:(NSCoder *)decoder{
theScores = [[decoder decodeObjectForKey:@"theScores"] retain];
return self;
}
-(void)dealloc{
for (Score* score in theScores){
[score release];
}
[theScores release];
[super dealloc];
}
@end
The implementation of the class Highscores shown in Listing 3-13 is pretty compact. The task
initWithDefaults initializes the NSMutableArray theScore and then fills theScores with ten new
Score objects. The task addScore: adds a new Score object to the theScores , sorts it by the score
achieved by the player, and then removes any extra Scores . This may result in the Score newScore
not actually being in the NSMutableArray theScores . However, it is implemented in this way so
the caller does not have to consider the fact that the theScore might not be high enough to be
considered an actual high score. The last two tasks, encodeWithCoder: and initWithCoder: ,
are from the protocol NSCoding . These tasks describe how a Highscores object is archived and
unarchived. Note that the object passed to both of these arguments is of the same type: NSCoder .
The class NSCoder provides tasks for encoding and decoding values. NSCoder is very much like
other iOS classes in that it presents a map-like interface for reading and writing data. In the task
encodeWithCoder: , we use the NSCoder task encodeObject:forKey: to write theScore object to
the encoder. We pass in a key value NSString that we will use in initWithCoder: to read the
theScores back out when we unarchive this class. Also note that the object that is returned from the
decodeObjectForKey: task is retained. This is done to make sure the object returned is not reclaimed
at some unspecified time.
When an NSMutableArray is encoded with an NSCoder , it knows to encode the elements in the array,
but those elements must know how to be encoded. Because theScores is an NSMutableArray filled
with Score objects, we have to tell the class Score how to encode and decode itself for this process
to work.
The Score Class
Score objects represent a date and score value. We have seen how the class Highscores manages a
list of Score objects. Let's take a quick look at this simple class. Listing 3-14 shows the header of the
Score class.
Listing 3-14. Score.h
#import<Foundation/Foundation.h>
@interface Score : NSObject <NSCoding>{
NSDate* date;
int score;
}