NSMutableDictionary Singleton issue

Question

I am coding Objective-C using the Cocos2D framework, and I have a singleton used for multiple purposes. One new purposes is to get and set character's "states" which are strings. I've recently made an NSDictionary for this purpose, but I have issues with the program freezing up when a method inside the singleton is called.

Here's the singleton code. I'm just leaving in the character state stuff:

.h

@interface ExGlobal : NSObject { 

    NSArray *charStates_keys;
    NSArray *charStates_objects;

    NSMutableDictionary *charStates;
} 

@property(nonatomic, retain) NSMutableDictionary *charStates;

+(ExGlobal*)sharedSingleton; 

- (NSString *)charState:(NSString *)charName;
- (void)set_charState:(NSString *)value forCharName:(NSString *)charName;

@end 

.m

#import "ExGlobal.h" 

@implementation ExGlobal 

@synthesize charStates;

static ExGlobal* _sharedSingleton = nil; 

+(ExGlobal*)sharedSingleton { 
    @synchronized([ExGlobal class]) {

        if (!_sharedSingleton) { 
            [[self alloc] init]; 
        } 

        return _sharedSingleton; 
    } 

    return nil; 
} 

+(id)alloc { 
    @synchronized([ExGlobal class]) { 

        NSAssert(_sharedSingleton == nil, @"Attempted to allocate a second instance of a singleton."); 
        _sharedSingleton = [super alloc]; 
        return _sharedSingleton; 

    } 

    return nil; 
} 

-(id)init { 
    self = [super init]; 
    if (self != nil) { 
        // initialize stuff here 

        exitName = @"ruinsSkyMid";

        sceneChangeKind = @"reborn";

        charStates = [[NSMutableDictionary alloc] init];

        charStates_keys = [NSArray arrayWithObjects:@"Feathers", @"Hummus", nil];

        charStates_objects = [NSArray arrayWithObjects:@"at wall", @"with Feathers", nil];

        charStates = [NSMutableDictionary dictionaryWithObjects:charStates_objects forKeys:charStates_keys];

    } 
    return self; 
} 


- (NSString *)charState:(NSString *)charName{

    NSString *value = [charStates objectForKey:charName];

    return value;

}

- (void)set_charState:(NSString *)charState forCharName:(NSString *)charName{

    [charStates setObject:charState forKey:charName];

}

- (void)dealloc {
    //I know it doesn't get called, but just in case
    [charStates release];

    [super dealloc];
}


@end 

It's unclear to me what exactly the issue is when it freezes. When this happens, all I get in the console is:

    Program received signal:  “EXC_BAD_ACCESS”.
warning: Unable to read symbols for /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.3.5 (8L1)/Symbols/Developer/usr/lib/libXcodeDebuggerSupport.dylib (file not found).
Previous frame inner to this frame (gdb could not unwind past this frame)
Previous frame inner to this frame (gdb could not unwind past this frame)

Which I'm sure doesn't help finding the issue. I found if I redefine charStates_keys, charStates_objects and charStates inside both the charState and set_charState methods, it seems to work without freezing, except set_charState does not change the state.

Answer 1

Not an answer as such but I didn't have enough space in the comments field above to post this, but it might be useful.

As bbum already said, your lack of retaining charStates is likely the problem.

If you are confused about when to retain and not retain objects there's a really good book called "Learn Objective-C on the Mac" and I know it's a Mac book but most of it applies to iPhone too. On page 171 of chapter 9 (Memory Management) it talks about the "Memory Management Rules" and how if you are confused about when to retain or not then you don't understand the simple rules of Objective C memory management.

Essentially if you create an object using new, alloc or copy, then the retain count is automatically set to 1 so the object is retained and does not require you to retain it and will require a subsequent release to deallocate.

If you create the object any other way then the object will be an autoreleased object.

Obviously these rules only apply within the standard iOS libraries and can't necessarily be applied to third party libraries.

I recommend anyone who doesn't fully understand memory management in Objective C read this book. I found highly enlightening even for my iPhone work.

Hope that helps/.

Answer 2

It isn't freezing, it is crashing. Hence the EXC_BAD_ACCESS. It looks like your Xcode installation is borked, too, as the two messages following should not happen.

Note that methods should not have _s in the name; not a cause of the problem, but a comment on following convention.

You aren't retaining charStates and that is likely the cause of the crash.