Init a NSMutableArray in a singelton that saves as a state - objective-c

Question

Im am using a pattern from the book Learning Cocos2D. I have a GameState class that is a singleton that can be saved as a state. The BOOL soundOn gets init as false the first time the class gest created, but the array levelProgress dosent. I made comments on all the lines on which I have tried to init the array.
The class uses a helper that loads and saves the data.
When i try 1 or 2 i get "instance variable 'levelProgress' accessed in class method" error.
#import <Foundation/Foundation.h>
#import "cocos2d.h"
#interface GameState : NSObject <NSCoding> {
BOOL soundOn;
NSMutableArray *levelProgress;
}
+ (GameState *) sharedInstance;
- (void)save;
#property (assign) BOOL soundOn;
#property (nonatomic, retain) NSMutableArray *levelProgress;
#end
#import "GameState.h"
#import "GCDatabase.h"
#implementation GameState
#synthesize soundOn;
#synthesize levelProgress;
static GameState *sharedInstance = nil;
+(GameState*)sharedInstance {
#synchronized([GameState class])
{
if(!sharedInstance) {
sharedInstance = [loadData(#"GameState") retain];
if (!sharedInstance) {
[[self alloc] init];
// 1. levelProgress = [[NSMutableArray alloc] init];
}
}
return sharedInstance;
}
return nil;
}
+(id)alloc
{
#synchronized ([GameState class])
{
NSAssert(sharedInstance == nil, #"Attempted to allocate a \
second instance of the GameState singleton");
sharedInstance = [super alloc];
// 2. levelProgress = [[NSMutableArray alloc] init];
return sharedInstance;
}
return nil;
}
- (void)save {
saveData(self, #"GameState");
}
- (void)encodeWithCoder:(NSCoder *)encoder {
// 3. levelProgress = [[NSMutableArray alloc] init];
[encoder encodeBool:currentChoosenCountry forKey:#"soundOn"];
[encoder encodeObject:levelProgress forKey:#"levelProgress"];
}
- (id)initWithCoder:(NSCoder *)decoder {
if ((self = [super init])) {
// 4. levelProgress = [[NSMutableArray alloc] init];
soundOn = [decoder decodeBoolForKey:#"soundOn"];
levelProgress = [decoder decodeObjectForKey:#"levelProgress"];
}
return self;
}
#end
Solution:
*I just added av init method...*
-(id)init {
self = [super init];
if (self != nil) {
levelProgress = [[NSMutableArray alloc] init];
}
return self;
}

Answer 1

Try this (this code may contain syntax or logic errors - I wrote it in notepad):
#interface GameState : NSObject <NSCoding>
#property (nonatomic, readwrite) BOOL soundOn;
#property (nonatomic, retain) NSMutableArray *levelProgress;
+ (GameState *)sharedState;
- (void)writeDataToCache;
#end
//
#implementation GameState
#synthesize soundOn, levelProgress;
#pragma mark - Singleton
static GameState *sharedState = nil;
+ (void)initialize {
static BOOL initialized = NO;
if (!initialized) {
initialized = YES;
if ([[NSFileManager defaultManager] fileExistsAtPath:[NSString stringWithFormat:#"%#/gameState", pathCache]]) {
NSData *encodedObject = [[NSData alloc] initWithContentsOfFile:[NSString stringWithFormat:#"%#/gameState", pathCache]];
data = [NSKeyedUnarchiver unarchiveObjectWithData:encodedObject];
}
else
data = [[GameState alloc] init];
}
}
+ (GameState *)sharedState {
return sharedState;
}
#pragma mark - Initialization
- (id)init {
if (self = [super init]) { // will be inited while application first run
soundOn = NO;
levelProgress = [[NSMutableArray alloc] init];
return self;
}
return nil;
}
#pragma mark - Coding Implementation
- (void)writeDataToCache { // use this method to save current state to cache
NSData *encodedObject = [NSKeyedArchiver archivedDataWithRootObject:self];
if([[NSFileManager defaultManager] fileExistsAtPath:[NSString stringWithFormat:#"%#/GameState", pathCache]])
[[NSFileManager defaultManager] removeItemAtPath:[NSString stringWithFormat:#"%#/GameState", pathCache] error:nil];
[[NSFileManager defaultManager] createFileAtPath:[NSString stringWithFormat:#"%#/GameState", pathCache] contents:encodedObject attributes:nil];
NSLog(#"GameState was saved successfully.");
}
- (void)encodeWithCoder:(NSCoder*)encoder {
[encoder encodeBool:self.soundOn forKey:#"soundOn"];
[encoder encodeObject:self.levelProgress forKey:#"levelProgress"];
}
- (id)initWithCoder:(NSCoder*)decoder {
if ((self = [super init])) {
self.soundOn = [decoder decodeBoolForKey:#"soundOn"];
self.levelProgress = [decoder decodeObjectForKey:#"levelProgress"];
NSLog(#"GameState was inited successfully");
return self;
}
return nil;
}
#end

Answer 2

1 & 2 are the same (and should not work, since levelProgress is an instance variable), 3 and 4 should be encoding/decoding the array, not initializing it anew.

Answer 3

1 and 2 are a mistake - you can't access instance variable without specifying an instance.
You can fix 1 by changing the line to sharedInstance.levelProgress = ....
2 is just a bad idea, you're breaking common convention of initializing using init... methods, it may surprise and cause problems for an other programmer who'll be working on the same code later.
3 and 4 are ok but if loadData fails they will not be executed and the object will be initialized with ordinary init and the array will be nil pointer:
[[self alloc] init];
you should also override init and initialize the properties there.