单例模式

static SinodisData *sharedInstance = nil;

@implementation SinodisData


#pragma mark -
#pragma mark singleton method

- (id)init {
	if (self = [super init]) {
		allProducts = [[NSMutableArray alloc] init];
		allRecipes = [[NSMutableArray alloc] init]; 
		allShoppinglist = [[NSMutableArray alloc] init];
	}	
	return self;
}

- (void)dealloc {	
	[super dealloc];
}

+ (SinodisData *)sharedInstance {
    @synchronized(self) {    
        if (sharedInstance == nil)
			sharedInstance = [[SinodisData alloc] init];
    }
    return sharedInstance;
}

+ (id)allocWithZone:(NSZone *)zone {
    @synchronized(self) {
        if (sharedInstance == nil) {
            sharedInstance = [super allocWithZone:zone];
            return sharedInstance;  
        }
    }
    return nil;
}

- (id)copyWithZone:(NSZone *)zone {
    return self;
}

- (id)retain {
    return self;
}

- (unsigned)retainCount {
    return UINT_MAX; 
}

- (void)release {
    //do nothing
}

- (id)autorelease {
    return self;
}