Encoding, decoding, and editing a NSMutableArray with NSCoding - ios

Question

I followed along with Ray Wenderlich's tutorial for saving game data using a singleton and NSCoding (http://www.raywenderlich.com/63235/how-to-save-your-game-data-tutorial-part-1-of-2). Everything they did I've been able to use for NSStrings (changing value, storing, using in my project). I tried to make an NSMutableArray so I could add to and save a list of strings, though, and it didn't work. There is probably a very simple solution to this, so thanks in advance for putting up with a newbie.
My code:
in RWGameData.h (my singleton for using game data):
#property (nonatomic, strong) NSMutableArray *dataArray;
in RWGameData.m, after #implementation:
static NSString* const GameDataArrayofValues = #"dataArray";
-(void)encodeWithCoder:(NSCoder *)encoder {
[encoder encodeObject:self.dataArray forKey:GameDataArrayofValues];
}
-(instancetype)initWithCoder:(NSCoder *)decoder {
self = [self init];
if (self) {
_dataArray = [[decoder decodeObjectForKey:GameDataArrayofValues] mutableCopy];
}
return self;
}
(there's also all the other code from that tutorial, like a save method etc.)
in myGame.m
[[RWGameData sharedGameData].dataArray addObject:#"objectString"];
[[RWGameData sharedGameData] save];
Logging the contents of the array right after this shows it as empty. [RWGameData sharedGameData].dataArray accepts the addObject call because I created it as an NSMutableArray, but it seems like it isn't actually going through.
Any ideas?

Answer 1

My guess is _dataArray is nil.
You should add code to your initWithCoder that checks to see if it was able to read array data. If not, _dataArray will be nil. In that case you should initialize an empty mutable array.
Your updated initWithCoder might look like this:
-(instancetype)initWithCoder:(NSCoder *)decoder {
self = [self init];
if (self)
{
_dataArray = [[decoder decodeObjectForKey:GameDataArrayofValues] mutableCopy];
if (_dataArray)
_dataArray = [[NSMutableArray alloc] init];
}
return self;
}
Likewise you need to implement a "regular" init method that sets _dataArray to an empty mutable array.