创建线程安全的单例（ARC或 非ARC）

一：创建 宏 文件 SynthesizeSingleton.h

SynthesizeSingleton.h

#if __has_feature(objc_arc) // ARC Version

#define SYNTHESIZE_SINGLETON_FOR_CLASS(classname)   

+ (classname *)shared##classname
{
    static classname *shared##classname = nil;
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        shared##classname = [[classname alloc] init];
    });
    return shared##classname;
}

#else // Non-ARC Version

#define SYNTHESIZE_SINGLETON_FOR_CLASS(classname) 
static classname *shared##classname = nil; 
+ (classname *)shared##classname 
{ 
    @synchronized(self) 
    { 
        if (shared##classname == nil) 
        { 
            shared##classname = [[self alloc] init]; 
        } 
    } 
    return shared##classname; 
} 

+ (id)allocWithZone:(NSZone *)zone 
{ 
@synchronized(self) 
{ 
if (shared##classname == nil) 
{ 
shared##classname = [super allocWithZone:zone]; 
return shared##classname; 
} 
} 
return nil; 
} 
- (id)copyWithZone:(NSZone *)zone 
{ 
return self; 
} 
- (id)retain 
{ 
return self; 
} 
- (NSUInteger)retainCount 
{ 
return NSUIntegerMax; 
} 
- (oneway void)release 
{ 
} 
- (id)autorelease 
{ 
return self; 
}

#endif

　　二：使用

MyClass.h

@interface MyClass : NSObject

+(DataStorage *)sharedMyClass;

@end
MyClass.m

#import "SynthesizeSingleton.h"
@implementation MyClass
SYNTHESIZE_SINGLETON_FOR_CLASS(MyClass)
@end

　参考资料