Singleton gets deallocated - objective-c

Question

I've created a simple singleton class to hold static data for my projects.
The first time I access this singleton is onEnter method in my Cocos2d scene. However when I try to access it again later in another method (same scene) this singleton is already released. I'm confused, how do I keep my singleton from being deallocated?
Here's my singleton's interface part:
#import <Foundation/Foundation.h>
#interface OrchestraData : NSObject
+(OrchestraData *)sharedOrchestraData;
#property (retain, readonly) NSArray *animalNames;
#end
Implementation:
#import "OrchestraData.h"
#implementation OrchestraData
#synthesize animalNames = animalNames_;
+(OrchestraData*)sharedOrchestraData
{
static dispatch_once_t pred;
static OrchestraData *_sharedOrchestraData = nil;
dispatch_once(&pred, ^{ _sharedOrchestraData = [[OrchestraData alloc] init]; });
return _sharedOrchestraData;
}
-(id)init {
if (self = [super init]) {
animalNames_ = [NSArray arrayWithObjects:#"giraffe", #"giraffe", #"giraffe", #"giraffe", nil];
}
return self;
}
#end
I'm using my singleton this way:
[[OrchestraData sharedOrchestraData] animalNames];
Update:
I took a fresh look into it with NSZombies enabled, it appears as if my NSArrays were released, not the singleton itself. What do I do?

Answer 1

You must implement your singleton in this way:
1) in .h file of your Singleton Class:
+ (SingletonClass *)instance;
2) in .m file:
+ (SingletonClass *)instance {
static SingletonClass* instance = nil;
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
instance = [[self alloc] init];
//your init code here
});
return instance;
}
If you want to call your singleton, just call [SingletonClass instance].
If your are interesting what is "dispatch_once_t", read about Grand Central Dispatch:
http://developer.apple.com/library/ios/#documentation/Performance/Reference/GCD_libdispatch_Ref/Reference/reference.html

Answer 2

RE Update:
Your NSArray deallocates because you're using the autorelease initializer arrayWithObjects and you assign it directly to the ivar animalNames_. Therefore it is not retained.
To fix this, assign the array to the property:
self.animalNames = [NSArray arrayWithObjects:#"giraffe", #"giraffe", #"giraffe", #"giraffe", nil];
Btw, under ARC this wouldn't have been an issue since the ivar would have been a strong (retaining) reference. I don't get tired encouraging anyone to switch to ARC. It's been available for well over a year now and there's absolutely no point in using MRC code anymore! It really pains me to see how developers still don't use the easier, faster, and straightforward option. (rant off) :)

Answer 3

You setup a pointer wherever you need it.
-(void)someMethod {
MySingleton *singleton = [MySingleton sharedSingleton];
singleton.data = YES; //dumb example to show you did something...
}
-(void)someOtherMethod {
MySingleton *singleton = [MySingleton sharedSingleton]; //You have to create a new pointer...
singleton.data = NO; //another dumber example to show you did something...
}
Note: this assumes that you have created a singleton the same way I have... your code might be different therefore causing my answer not to apply...

Answer 4

You need to overwrite the below method inside your singleton class, because in your program, if someone has initialised [[SingletonClass alloc] init] then singleton will have another instance and release it will cause an error.
+ (id)allocWithZone:(NSZone *)zone{
return [[self SingletonClass] retain];
}
- (id)copyWithZone:(NSZone *)zone{
return self;
}
- (id)retain{
return self;
}