obejec-c單例類宏

在使用object-c編程的時候，常常需要使用單例類來訪問全局變量，每次重寫都比較麻煩，有了宏就好多了

#import <objc/runtime.h>

#define CWL_DECLARE_SINGLETON_FOR_CLASS_WITH_ACCESSOR(classname, accessorMethodName) \
+ (classname *)accessorMethodName;

#if __has_feature(objc_arc)
#define CWL_SYNTHESIZE_SINGLETON_RETAIN_METHODS
#else
#define CWL_SYNTHESIZE_SINGLETON_RETAIN_METHODS \
- (id)retain \
{ \
return self; \
} \
\
- (NSUInteger)retainCount \
{ \
return NSUIntegerMax; \
} \
\
- (oneway void)release \
{ \
} \
\
- (id)autorelease \
{ \
return self; \
}
#endif

//實現單例類
#define CWL_SYNTHESIZE_SINGLETON_FOR_CLASS_WITH_ACCESSOR(classname, accessorMethodName) \
\
static classname *accessorMethodName##Instance = nil; \
\
+ (classname *)accessorMethodName \
{ \
@synchronized(self) \
{ \
if (accessorMethodName##Instance == nil) \
{ \
accessorMethodName##Instance = [super allocWithZone:NULL]; \
accessorMethodName##Instance = [accessorMethodName##Instance init]; \
method_exchangeImplementations(\
class_getClassMethod([accessorMethodName##Instance class], @selector(accessorMethodName)),\
class_getClassMethod([accessorMethodName##Instance class], @selector(cwl_lockless_##accessorMethodName)));\
method_exchangeImplementations(\
class_getInstanceMethod([accessorMethodName##Instance class], @selector(init)),\
class_getInstanceMethod([accessorMethodName##Instance class], @selector(cwl_onlyInitOnce)));\
} \
} \
\
return accessorMethodName##Instance; \
} \
\
+ (classname *)cwl_lockless_##accessorMethodName \
{ \
return accessorMethodName##Instance; \
} \
\
+ (id)allocWithZone:(NSZone *)zone \
{ \
return [self accessorMethodName]; \
} \
\
- (id)copyWithZone:(NSZone *)zone \
{ \
return self; \
} \
- (id)cwl_onlyInitOnce \
{ \
return self;\
} \
\
CWL_SYNTHESIZE_SINGLETON_RETAIN_METHODS

#define CWL_DECLARE_SINGLETON_FOR_CLASS(classname) \
CWL_DECLARE_SINGLETON_FOR_CLASS_WITH_ACCESSOR(classname, shared##classname)
#define CWL_SYNTHESIZE_SINGLETON_FOR_CLASS(classname) \
CWL_SYNTHESIZE_SINGLETON_FOR_CLASS_WITH_ACCESSOR(classname, shared##classname)

使用很方便，在頭文件中使用

CWL_DECLARE_SINGLETON_FOR_CLASS（MyClass）

在實現文件中

CWL_SYNTHESIZE_SINGLETON_FOR_CLASS（MyClass）