IOS 中两种单例模式的写法实例详解

#import "ServiceManager.h"static ServiceManager *defaultManager;@implementation ServiceManager+(ServiceManager *)defaultManager{  if(!defaultManager)    defaultManager=[[self allocWithZone:NULL] init];  return defaultManager;}@end

#import "ServiceManager.h"@implementation ServiceManager+(ServiceManager *)sharedManager{  static dispatch_once_t predicate;  static ServiceManager * sharedManager;  dispatch_once(&predicate, ^{    sharedManager=[[ServiceManager alloc] init];  });  return sharedManager;}@end