iOS开发学习

iOS 单例模式

2017-05-30  本文已影响9人  BEYOND黄

单例模式的作用:可以保证在程序运行过程,一个类只有一个实例,而且该实例易于供外界访问,从而方便地控制了实例个数,并节约系统资源。

单例模式的使用场合:在整个应用程序中,共享一份资源(这份资源只需要创建初始化1次)

ARC中,单例模式的实现

在.m中保留一个全局的static的实例

static id _instance;

重写allocWithZone:方法,在这里创建唯一的实例(注意线程安全)

+ (instancetype)allocWithZone:(struct _NSZone *)zone

{

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

_instance = [super allocWithZone:zone];

});

return _instance;}

提供1个类方法让外界访问唯一的实例

+ (instancetype)sharedInstance

{

static dispatch_once_t onceToken;

dispatch_once(&onceToken, ^{

_instance = [[self alloc] init];

});

return _instance;

}

实现copyWithZone:方法

- (id)copyWithZone:(struct _NSZone *)zone

{

return _instance;

}

单例模式通用宏

#define SingleH(name) +(instancetype)share##name;

#if __has_feature(objc_arc)

//条件满足 ARC

#define SingleM(name) static id _instance;\

+(instancetype)allocWithZone:(struct _NSZone *)zone\

{\

static dispatch_once_t onceToken;\

dispatch_once(&onceToken, ^{\

_instance = [super allocWithZone:zone];\

});\

\

return _instance;\

}\

\

+(instancetype)share##name\

{\

return [[self alloc]init];\

}\

\

-(id)copyWithZone:(NSZone *)zone\

{\

return _instance;\

}\

\

-(id)mutableCopyWithZone:(NSZone *)zone\

{\

return _instance;\

}

#else

//MRC

#define SingleM(name) static id _instance;\

+(instancetype)allocWithZone:(struct _NSZone *)zone\

{\

static dispatch_once_t onceToken;\

dispatch_once(&onceToken, ^{\

_instance = [super allocWithZone:zone];\

});\

\

return _instance;\

}\

\

+(instancetype)share##name\

{\

return [[self alloc]init];\

}\

\

-(id)copyWithZone:(NSZone *)zone\

{\

return _instance;\

}\

\

-(id)mutableCopyWithZone:(NSZone *)zone\

{\

return _instance;\

}\

-(oneway void)release\

{\

}\

\

-(instancetype)retain\

{\

return _instance;\

}\

\

-(NSUInteger)retainCount\

{\

return MAXFLOAT;\

}

#endif

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