Singleton Instance in Objective-C

Singleton Instance in Objective-C

#pragma mark
#pragma mark Singleton Instance--
static AppManager *sharedSingleton_ = nil;

// Get the shared instance and create it if necessary.
+ (AppManager *) sharedInstance{
    if (sharedSingleton_ == nil){
        @synchronized(self){
            //double checking.
            if (sharedSingleton_ == nil) {
                sharedSingleton_ = [NSAllocateObject([self class], 0, NULL) init];
            }
        }
    }
    return sharedSingleton_;
}
// We don't want to allocate a new instance, so return the current one.
+ (id) allocWithZone:(NSZone *)zone{
    //return instance
    return [[self sharedInstance] retain];
}
// Equally, we don't want to generate multiple copies of the singleton.
- (id) copyWithZone:(NSZone*)zone{
    return self;
}
// 
- (id) retain{
    return self;
}

- (NSUInteger) retainCount{
    // denotes an object that cannot be released
    return NSUIntegerMax; 
}

// This function is empty, as we don't want to let the user release this object.
- (oneway void)release {
    
}

//Do nothing, other than return the shared instance - as this is expected from autorelease.
- (id)autorelease {
    return self;
}

// Your dealloc method will never be called, as the singleton survives for the duration of your app.
// However, I like to include it so I know what memory I'm using (and incase, one day, I convert away from Singleton).
-(void)dealloc{
    [super dealloc];

}