Initializing a static singleton object with NSCoder

Question

I'm working on an iPhone app and facing some troubles with my shared singleton class. I'm using a shared singleton to store two variables int gameRuns and int totalScore 'gamRuns' just increments every time the user loads the app, and 'totalScore' is obvious :D

the issue is as follows, I load the singleton and init using my own method when the app loads using this code:

+ (SingletonLevelState*)sharedLevelStateInstance {

static SingletonLevelState *sharedLevelStateInstance;

@synchronized(self) {
    if(!sharedLevelStateInstance) {
        //Init a singleton
        sharedLevelStateInstance = [[SingletonLevelState alloc] init];
        sharedLevelStateInstance->gameRuns = 1;
        sharedLevelStateInstance->totalScore = 0;
    }
}
return sharedLevelStateInstance;
}

This is working great as I can reference this class from any other class and always get a pointer to the same object, so this works fine from other objects:

sharedLevelState = [SingletonLevelState sharedLevelStateInstance];
sharedLevelStateInstance.gameRuns++;

Now I added the NSCoder protocol, and added the two methods initWithCoder and encodeWithCoder as follows :

- (void) encodeWithCoder: (NSCoder *)coder
{
    //encode level data
    [coder encodeInt:self->gameRuns forKey:@"gameRuns"];
    [coder encodeInt:self->totalScore forKey:@"totalScore"];
}
- (id) initWithCoder: (NSCoder *) coder
{
    if(self = [super init]){
        self->gameRuns = [coder decodeIntForKey:@"gameRuns"];
        self->totalScore = [coder decodeIntForKey:@"totalScore"];
    }
    return self;
}

Now when the app loads, I check to see if we already have a saved sate, if it exists, I just unarchive the class with that file, if not, I init that class using my custom method above, then set its defaults, encode it to file so we have a saved state, here's the code:

 //Load Level state
sharedLevelStateInstance = [SingletonLevelState sharedLevelStateInstance];

//Check if file is saved
NSFileManager *fm = [[NSFileManager alloc] init];
NSString *gameStatePath = [NSString stringWithString:[self getSavePath]];

if([fm fileExistsAtPath:gameStatePath]){
    [self loadState];
    sharedLevelStateInstance.gameRuns = sharedLevelStateInstance.gameRuns+1;
    NSLog(@"Loaded %d times", [sharedLevelStateInstance gameRuns]);
}
[fm release];

Now the last line in the if statement works perfectly, it increments every time I load the app as expected and I feel really happy lol.

However, the problem arises when I try to get a reference of the singleton in another class by doing the following:

sharedLevelStateInstance = [SingletonLevelState sharedLevelStateInstance];
NSLog(@"Played: %d times", sharedLevelStateInstance.gameRuns);

It always counts back to 1, I know what happens but I'm not sue what's the best way to solve it, when I initWithCoder the singleton, It's not returning a static object, it creates a new one, when I init my sharedLevelStateInstance, it calls my first custom method, initializing it to the defaults hardcoded.

So StackOverflow, can you please help me ?!

I just need to know what's the best way to get a reference to the same object without allocating a new one every time I initWithCoder !

Thanks :)

Answer 1

So, you code should probably look like this:

if(self = [[SingletonLevelState sharedLevelStateInstance] retain])

Which sets the variables of the singleton, and returns the singleton. Be sure to retain the singleton, so that when the NSCoder releases this instance, it doesn't fully deallocate your singleton.