Advice on High Score persistence (iPhone, Cocoa Touch)

Question

I was curious what is considered the better way to manage the reading and writing of a High Score plist file. My High Score class is:

@interface HighScore : NSObject <NSCoding> {
    NSString        *name;
    int             score;
    int             level;
    int             round;
    NSDate          *date;
}

Now, I could do method A, add NSCoding methods:

- (void) encodeWithCoder: (NSCoder *) coder {
    [coder encodeObject: name
                 forKey: kHighScoreNameKey];
    [coder encodeInt: score
              forKey: kHighScoreScoreKey];
    [coder encodeInt: level
              forKey: kHighScoreLevelKey];
    [coder encodeInt: round
              forKey: kHighScoreRoundKey];
    [coder encodeObject: date
                 forKey: kHighScoreDateKey];
} // encodeWithCoder

- (id) initWithCoder: (NSCoder *) decoder {
    if (self = [super init]) {
        self.name = [decoder decodeObjectForKey: kHighScoreNameKey];
        self.score = [decoder decodeIntForKey: kHighScoreScoreKey];
        self.level = [decoder decodeIntForKey: kHighScoreLevelKey];
        self.round = [decoder decodeIntForKey: kHighScoreRoundKey];
        self.date = [decoder decodeObjectForKey: kHighScoreDateKey];
    }
    return (self);
} // initWithCoder

And write it all out with:

if (![NSKeyedArchiver archiveRootObject:highScoresList toFile:path]) ...

Reading it back in would be pretty straight forward. However the plist file, IMHO, looks like crap.

Or I could employ method B:

NSMutableArray *array = [NSMutableArray arrayWithCapacity:20];;
for (HighScore *hs in highScoresList) {
    NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:
                          hs.name, kHighScoreNameKey,
                          [NSNumber numberWithInteger:hs.score], kHighScoreScoreKey,
                          [NSNumber numberWithInteger:hs.level], kHighScoreLevelKey,
                          [NSNumber numberWithInteger:hs.round], kHighScoreRoundKey,
                          hs.date, kHighScoreDateKey,
                          nil];
    [array addObject:dict];
    [dict release];
}

and write it all out with:

if (![array writeToFile:path atomically:YES]) ...

Reading it back in is a tiny bit harder. But the plist file looks much cleaner (smaller and compact).

Any thoughts? Am I missing something that is much simpler? (I want to keep the High Scores separate from NSUserDefaults so I am not using that).

Answer 1

Both your ways look fine to me. There is also Core Data in the 3.0 OS, although it might be overkill if all you want to save is a single high score value.

Answer 2

I'm not sure that I understand your objections! Both should work just fine.

Personally I prefer method A. I think it makes sense that an object knows how to encode itself. It makes maintenance easier and any changes more localised. Plus it probably uses less memory.

Answer 3

check out this question, maybe it's useful for your app

Answer 4

I went with method B because: 1. The plist file is more readable and 2. I can save off some file and class version numbering into this method easily:

In my HighScore class:

- (id)initFromDictionary: (NSDictionary *)dict;
{
    if (self = [super init]) {
        self.name = [dict objectForKey:kHighScoreNameKey];
        self.score = [[dict objectForKey:kHighScoreScoreKey] integerValue];
        self.game = [[dict objectForKey:kHighScoreGameKey] integerValue];
        self.level = [[dict objectForKey:kHighScoreLevelKey] integerValue];
        self.date = [dict objectForKey:kHighScoreDateKey];
    }
    return (self);
}
- (NSDictionary *)putIntoDictionary;
{
    NSDictionary *dict = [[NSDictionary alloc] initWithObjectsAndKeys:
                          name, kHighScoreNameKey,
                          [NSNumber numberWithInt:score], kHighScoreScoreKey,
                          [NSNumber numberWithInt:game], kHighScoreGameKey,
                          [NSNumber numberWithInt:level], kHighScoreLevelKey,
                          date, kHighScoreDateKey,
                          nil];
    return dict;
}

And in my HighScoreTable class:
- (id) load
{
    NSString *path = [self getFilePath];

//  [self clear];
    NSDictionary *rootLevelPlistDict = [NSDictionary dictionaryWithContentsOfFile:path];
    int versNum = [[rootLevelPlistDict objectForKey:kHighScoreVersKey] integerValue];

    if (versNum == kHighScoreVersNum) {
        NSArray *insideArray = [rootLevelPlistDict objectForKey:kHighScoresKey];

        NSDictionary *dict;
        for (dict in insideArray) {
            HighScore *hs = [[HighScore alloc] initFromDictionary:dict];
            [highScoresList addObject:hs];
            [hs release];
        }
    }
    return sharedHighScoresSingleton;
}


- (void) save
{   
    if (!changed)
        return;
    NSString *path = [self getFilePath];
    NSMutableArray *array = [NSMutableArray arrayWithCapacity:kNumberOfHighScores];
    for (HighScore *hs in highScoresList) {
        NSDictionary *dict = [hs putIntoDictionary];
        [array addObject:dict];
        [dict release];
    }
    NSDictionary *rootLevelPlistDict = [[NSDictionary alloc] initWithObjectsAndKeys: 
            [[[NSBundle mainBundle] infoDictionary]
                objectForKey:(NSString*)kCFBundleNameKey], kHighScoreAppNameKey,
                [NSNumber numberWithInt:kHighScoreHeaderVersNum], kHighScoreHeaderVersKey,
                [NSNumber numberWithInt:kHighScoreVersNum], kHighScoreVersKey,
                [NSDate date], kHighScoreCreationKey,
             array, kHighScoresKey,
             nil];

    if (![rootLevelPlistDict writeToFile:path atomically:YES])
        NSLog(@"not successful in writing the high scores");
    [rootLevelPlistDict release];
}