iOS 单例

Objective-C 单例宏

#define SINGLETON_SHARED + (instancetype)shared;

#define SINGLETON_METHOD(ClassName) \
+ (id)allocWithZone:(struct _NSZone *)zone { \
    static ClassName *_shared = nil;\
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _shared = [super allocWithZone:zone]; \
    }); \
    return _shared; \
} \
\
+ (instancetype)shared { \
    return [[[self class] alloc] init];\
}

Swift 单例声明

class Singleton {
    // 单例 shared
    static let shared = Singleton()
    
   // 私有init
    private init(){}
    
}

// 继承自 NSObject
class SingletonObject: NSObject {

   // 单例 shared
    static let shared = SingletonObject()
    
   // 私有init
    private override init() {}
    
   // 不操作返回本身
    override func copy() -> Any {
        return self
    }
  
    // 不操作返回本身
    override func mutableCopy() -> Any {
        return self
    }
}