單例設計模式

非ARC項目中，單獨文件修改成ARC：

項目－Build Phases － Compile Sources － 找到要修改的文件名稱，雙擊，－ 寫入"-fobjc-arc"。

MRC

#import "Sound.h"

@implementation Sound

static Sound *_soundTool = nil;

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

    if (_soundTool == nil) {

        static dispatch_once_t onceToken;

        dispatch_once(&onceToken, ^{

            _soundTool = [super allocWithZone:zone];

        });

    }

    return _soundTool;

}

- (instancetype)init {

    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{

        _soundTool = [super init];

    });

    return _soundTool;

}

- (oneway void)release {

    

}

- (instancetype)retain {

    return  self;

}

- (NSUInteger)retainCount {

    return 1;

}

+(instancetype)shared {

    return [[self alloc]init];

}

@end

ARC 

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

    if (_instance == nil) {

        static dispatch_once_t onceToken;

        dispatch_once(&onceToken, ^{

            _instance = [super allocWithZone:zone];

        });

    }

    return _instance;

}

- (instancetype)init {

    static dispatch_once_t onceToken;

    dispatch_once(&onceToken, ^{

        _instance = [super init];

    });

    return _instance;

}

+ (instancetype)sharedSoundTool {

    return [[self alloc] init];

}

Singleton.h 文件，能夠直接使用。適用於MRC和ARC

// 幫助實現單例設計模式

// .h文件的實現

#define SingletonH(methodName) + (instancetype)shared##methodName;

// .m文件的實現

#if __has_feature(objc_arc) // 是ARC

#define SingletonM(methodName) \

static id _instace = nil; \

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

{ \

if (_instace == nil) { \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

_instace = [super allocWithZone:zone]; \

}); \

} \

return _instace; \

} \

\

- (id)init \

{ \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

_instace = [super init]; \

}); \

return _instace; \

} \

\

+ (instancetype)shared##methodName \

{ \

return [[self alloc] init]; \

} \

+ (id)copyWithZone:(struct _NSZone *)zone \

{ \

return _instace; \

} \

\

+ (id)mutableCopyWithZone:(struct _NSZone *)zone \

{ \

return _instace; \

}

#else // 不是ARC

#define SingletonM(methodName) \

static id _instace = nil; \

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

{ \

if (_instace == nil) { \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

_instace = [super allocWithZone:zone]; \

}); \

} \

return _instace; \

} \

\

- (id)init \

{ \

static dispatch_once_t onceToken; \

dispatch_once(&onceToken, ^{ \

_instace = [super init]; \

}); \

return _instace; \

} \

\

+ (instancetype)shared##methodName \

{ \

return [[self alloc] init]; \

} \

\

- (oneway void)release \

{ \

\

} \

\

- (id)retain \

{ \

return self; \

} \

\

- (NSUInteger)retainCount \

{ \

return 1; \

} \

+ (id)copyWithZone:(struct _NSZone *)zone \

{ \

    return _instace; \

} \

 \

+ (id)mutableCopyWithZone:(struct _NSZone *)zone \

{ \

    return _instace; \

}

#endif