单例的几种方式

1、GCD

static TXPerson *_person;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _person = [super allocWithZone:zone];
    });
    return _person;
}

+ (instancetype)sharedPerson
{
    static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        _person = [[self alloc] init];
    });
    return _person;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _person;
}

2、非GCD

static id _instance;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
    @synchronized(self) {
        if (_instance == nil) {
            _instance = [super allocWithZone:zone];
        }
    }
    return _instance;
}

+ (instancetype)sharedInstance
{
    @synchronized(self) {
        if (_instance == nil) {
            _instance = [[self alloc] init];
        }
    }
    return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
    return _instance;
}

3、宏-1

// .h文件
#define TXXMGSingletonH + (instancetype)sharedInstance;

// .m文件
#define SingletonM \
static id _instace; \
 \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instace = [super allocWithZone:zone]; \
    }); \
    return _instace; \
} \
 \
+ (instancetype)sharedInstance \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instace = [[self alloc] init]; \
    }); \
    return _instace; \
} \
 \
- (id)copyWithZone:(NSZone *)zone \
{ \
    return _instace; \
}

4、宏-2

// .h文件
#define TXSingletonH(name) + (instancetype)shared##name;

// .m文件
#define SingletonM(name) \
static id _instance; \
 \
+ (instancetype)allocWithZone:(struct _NSZone *)zone \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instance = [super allocWithZone:zone]; \
    }); \
    return _instance; \
} \
 \
+ (instancetype)shared##name \
{ \
    static dispatch_once_t onceToken; \
    dispatch_once(&onceToken, ^{ \
        _instance = [[self alloc] init]; \
    }); \
    return _instance; \
} \
 \
- (id)copyWithZone:(NSZone *)zone \
{ \
    return _instance; \
}

在使用的时候
TXSingletonH(Person)
TXSingletonM(Person)
就是说把Person接在了后边。

注意宏中#的使用
##表示连接
@#mudy，表示@"mudy",即将紧跟在后边的标识符加上字符串