1.MBProgressHUD的下载地址
2.值得借鉴的代码
#ifndef MB_INSTANCETYPE
#if __has_feature(objc_instancetype)
#define MB_INSTANCETYPE instancetype
#else
#define MB_INSTANCETYPE id
#endif
#endif
#ifndef MB_STRONG
#if __has_feature(objc_arc)
#define MB_STRONG strong
#else
#define MB_STRONG retain
#endif
#endif
#ifndef MB_WEAK
#if __has_feature(objc_arc_weak)
#define MB_WEAK weak
#elif __has_feature(objc_arc)
#define MB_WEAK unsafe_unretained
#else
#define MB_WEAK assign
#endif
#endif
#if NS_BLOCKS_AVAILABLE
typedef void (^MBProgressHUDCompletionBlock)();
#endif
