Properly restarting/re-initializing a semi-singleton - ios

Question

I'm using the semi-singleton approach for the main game layer/scene of my cocos2d game as shown in the later code.
The objective is to properly restart/recreate this singleton scene using a button in a pause or gameover layers by calling: [[GameLayer sharedGameLayer] restart] method.
The problem is if I use a CCTransition effect for that, and override the GameLayer's dealloc method with sharedGameLayer = nil; line (to ensure the resetting of the static variable), the sharedGameLayer variable stays nil after the first restart (aka. after the first dealloc), so calling the restart method does nothing.
What works with suspicion is not to override the dealloc method at all, but before restarting the scene using replaceScene:, I set the sharedGameLayer to nil.
Question: Is this the right approach for restarting/recreating this semi-singleton class?
Thanks in advance.
Code:
GameLayer.m:
static GameLayer *sharedGameLayer;
#implementation GameLayer
- (id)init
{
NSLog(#"%s", __PRETTY_FUNCTION__);
// always call "super" init
// Apple recommends to re-assign "self" with the "super's" return value
if (self = [super initWithColor:ccc4(255, 255, 255, 255) width:[CCDirector sharedDirector].winSize.width
height:[CCDirector sharedDirector].winSize.height])
{
// Set the sharedGameLayer instance to self.
sharedGameLayer = self;
// Set the initial game state.
self.gameState = kGameStateRunning;
// Register with the notification center in order to pause the game when game resigns the active state.
NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
[center addObserver:self selector:#selector(pauseGame) name:UIApplicationWillResignActiveNotification object:nil];
// Enable touches and multi-touch.
CCDirector *director = [CCDirector sharedDirector];
[director.touchDispatcher addTargetedDelegate:self priority:0 swallowsTouches:YES];
director.view.multipleTouchEnabled = YES;
// Set the initial score.
self.score = 5;
// Create the spiders batch node.
[self createSpidersBatchNode];
// Load the game assets.
[self loadAssets];
// Play Background music.
if (![SimpleAudioEngine sharedEngine].isBackgroundMusicPlaying)
[[SimpleAudioEngine sharedEngine] playBackgroundMusic:#"backgroundmusic.mp3" loop:YES];
// Preload sound effects.
[[SimpleAudioEngine sharedEngine] preloadEffect:#"inbucket.mp3"];
[[SimpleAudioEngine sharedEngine] preloadEffect:#"outbucket.mp3"];
[[SimpleAudioEngine sharedEngine] preloadEffect:#"gameover.mp3"];
// Schdule updates.
[self scheduleUpdate];
[self schedule:#selector(releaseSpiders) interval:0.7];
}
return self;
}
- (void)createSpidersBatchNode
{
NSLog(#"%s", __PRETTY_FUNCTION__);
// BatchNode. (For Animation Optimization)
self.spidersBatchNode = [CCSpriteBatchNode batchNodeWithFile:#"spiderAtlas.png"];
// Spider sprite + BatchNode + animation action.
for (int i = 0; i < 50; i++) {
Spider *spider = [[Spider alloc] init];
spider.spiderSprite.visible = NO;
}
[self addChild:self.spidersBatchNode];
}
- (void)restartGame
{
// Play button pressed sound effect.
[[SimpleAudioEngine sharedEngine] playEffect:#"button.mp3"];
// Nil'ing the static variable.
sharedGameLayer = nil;
// Restart game.
[[CCDirector sharedDirector] replaceScene:[CCTransitionFade transitionWithDuration:1.0 scene:[GameLayer scene]]];
}
+ (CCScene *)scene
{
// 'scene' is an autorelease object.
CCScene *scene = [CCScene node];
// Game Layer.
// 'gameLayer' is an autorelease object.
GameLayer *gameLayer = [GameLayer node];
// add gameLayer as a child to scene
[scene addChild: gameLayer];
// HUD Layer.
HUDLayer *hudLayer = [HUDLayer node];
[scene addChild:hudLayer];
gameLayer.hud = hudLayer;
// return the scene
return scene;
}
+ (GameLayer *)sharedGameLayer
{
return sharedGameLayer;
}
- (void)cleanup
{
[[NSNotificationCenter defaultCenter] removeObserver:self];
[[CCDirector sharedDirector].touchDispatcher removeDelegate:self];
[self stopAllActions];
[self unscheduleAllSelectors];
[self unscheduleUpdate];
[self removeAllChildrenWithCleanup:YES];
self.hud = nil;
[super cleanup];
}
//- (void)dealloc
//{
// sharedGameLayer = nil;
//}
#end

Answer 1

I bet your new game layer is created before the first one deallocates, therefore it sets the static var to nil. Check that sharedGameLayer equals self in dealloc.

Answer 2

Do not use dealloc to set the static variable to nil. Dealloc happens after your object has stopped being used. Never use it for controlling the behaviour of your app.
For all you know, 30 minutes might have passed between when you set sharedGameLayer to nil and when the dealloc method gets called. Or perhaps dealloc will never be called at all.
Your code looks good, just delete the commented out "dealloc" code.
Also, this code:
[[NSNotificationCenter defaultCenter] removeObserver:self];
Should be done in the -dealloc method in addition to your custom -cleanup method. It is perfectly fine to remove an observer twice, if it's already been removed nothing will happen.
Another note, +sharedGameLayer should return a variable of type instancetype and it should be responsible for setting the sharedGameLayer variable. If you sharedGameLayer inside -init, you will run into bugs.
For example:
+ (instancetype)sharedGameLayer
{
if (sharedGameLayer)
return sharedGameLayer;
sharedGameLayer = [[[self class] alloc] init];
return sharedGameLayer;
}
- (id)init
{
if (!(self = [super init]))
return nil;
.
.
.
return self;
}