1、release时，屏蔽log #if defined (DEBUG) && DEBUG == 1    #else  #define NSLog(...) {};  #endif   2、在主线程或在后台执行block#define BACK(block) dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), block)  #define MAIN(block) dispatch_async(dispatch_get_main_queue(),block)   3、设备相关 #define isRetina ([UIScreen instancesRespondToSelector:@selector(currentMode)] ? CGSizeEqualToSize(CGSizeMake(640, 960), [[UIScreen mainScreen] currentMode].size) : NO)    #define iPhone5 ([UIScreen instancesRespondToSelector:@selector(currentMode)] ? CGSizeEqualToSize(CGSizeMake(640, 1136), [[UIScreen mainScreen] currentMode].size) : NO)    #define isPad (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad)    #define CurrentSystemVersion ([[UIDevice currentDevice] systemVersion])    #define CurrentLanguage ([[NSLocale preferredLanguages] objectAtIndex:0])    4、区分模拟器和真机#if TARGET_OS_IPHONE  //iPhone Device  #endif    #if TARGET_IPHONE_SIMULATOR  //iPhone Simulator  #endif   5、根据是否使用ARC做不同操作#if __has_feature(objc_arc)      //compiling with ARC  #else      // compiling without ARC  #endif

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