单例模式是开发中最常用的写法之一,iOS的单例模式有两种官方写法,如下:
不使用GCD
#import "ServiceManager.h" static ServiceManager *defaultManager; @implementation ServiceManager +(ServiceManager *)defaultManager{ if(!defaultManager) defaultManager=[[self allocWithZone:NULL] init]; return defaultManager; } @end
使用GCD
#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
dispatch_once这个函数, 它可以保证整个应用程序生命周期中某段代码只被执行一次!