iOS单例两种创建方式

1、GCD方式创建单例

static id _instance;

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

{

static dispatch_once_t onceToken;

dispatch_once(&onceToken,^{

_instance =[superallocWithZone:zone];

});

return_instance;

}

+(instancetype)sharedInstance

{

static dispatch_once_t onceToken;

dispatch_once(&onceToken,^{

_instance =[[self alloc]init];

});

return_instance;

}

-(id)copyWithZone:(NSZone *)zone

{

return_instance;

}

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

return_instance;

}

2、互斥锁方式

static id _instance;

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

{

@synchronized(self){

if(_instance == nil){

_instance =[superallocWithZone:zone];

}

}

return_instance;

}

+(instancetype)sharedInstance

{

@synchronized(self){

if(_instance == nil){

_instance =[[self alloc]init];

}

}

return_instance;

}

-(id)copyWithZone:(NSZone *)zone

{

return_instance;

}