iOS 创建单例的两种方法(MRC ARC)

MRC
static AccountManager *DefaultManager = nil;

+ (AccountManager *)defaultManager {
if (!DefaultManager) DefaultManager = [[self allocWithZone:NULL] init];
return DefaultManager;
}

ARC
+ (AccountManager *)sharedManager
{
static AccountManager *sharedAccountManagerInstance = nil;
static dispatch_once_t predicate;
dispatch_once(&predicate, ^{
sharedAccountManagerInstance = [[self alloc] init];
});
return sharedAccountManagerInstance;
}