iOS开发笔记-两种单例模式的写法

Changwei | 3/20/2015 3:48:00 PM


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!