How to archive and unarchive an NSObject? - ios

Question

I am trying to archive an NSObject that I send through match data in a game center turn based game.
Below is my code for archiving my object
turnDataObject MyData = [[turnDataObject alloc] init];
data = [NSKeyedArchiver archivedDataWithRootObject:MyData];
This is my code for unarchiving my object
readMyData = [NSKeyedUnarchiver unarchiveObjectWithData:data] ;
However when I run this code I get an error
thread 1 exc bad access code
I think that this might have to do with sending addresses when I archive data. How do I send something that will be readable when I unarchive it?
Edit 1: I get the error on the next line after I unarchive. it says that the adress I am trying to access is null. I remember reading somewhere that I souldn't send adresses of my NSObject but I am not sure how to convert it to something else.
readMyData = [NSKeyedUnarchiver unarchiveObjectWithData:data] ;
NSLog(#"current game happens to be: %#", readMyData.currentGame);
Edit 2: here is my init with coder and encode with coder
- (instancetype)initWithCoder:(NSCoder *)decoder
{
self = [self init];
if (self) {
_currentGame = [decoder decodeObjectForKey:currentGameDataKey];
}
return self;
}
- (void)encodeWithCoder:(NSCoder *)encoder
{
//scores data keys
[encoder encodeObject:self.currentGame forKey:currentGameDataKey];
}
Edit 3: _currentGame is in my objects .h file
#property (assign, nonatomic) NSString *currentGame;

Answer 1

I would suggest creating NSKeyedArchiver and NSKeyedUnarchiver objects and using those instead of using the type (which it looks like you're doing.)
I usually program in Swift but here's a shot at example code:
theArchiver NSKeyedArchiver = [[theArchiver alloc] init];
data = [theArchiver archivedDataWithRootObject:MyData];
Then you would do the same thing with the NSKeyedUnarchiver.

Answer 2

Your initWithCoder implementation is wrong:
self = [self init];
That should be:
self = [super init];

Answer 3

You need to add NSCoding protocol to MyData Class, here is the code snippet with supporting NSCoding in order to add Archiving support to NSObjet.
MyData.h
#interface MyData : NSObject <NSCoding>
#property (nonatomic, strong) NSString *currentGame;
#end
MyData.m
//This method is optional, if you need constructor for current game
- (instancetype)initWithCurrentGame:(NSDictionary *)currentGame {
self = [super init];
if (self) {
self.currentGame = currentGame;
}
return self;
}
-(void)encodeWithCoder:(NSCoder *)encoder {
[encoder encodeObject:self.currentGame forKey:#"currentGame"];
}
-(id)initWithCoder:(NSCoder *)decoder {
self.currentGame = [decoder decodeObjectForKey:#"currentGame"];
return self;
}