iOS arc和非arc 适用 宏

+ (void)showAlertWithMessage:(NSString *)messages
{
    dispatch_async(dispatch_get_main_queue(), ^{
        UIAlertView *alert = [[UIAlertView alloc]initWithTitle:@"版本更新提示" message:messages delegate:nil cancelButtonTitle:@"确定" otherButtonTitles:nil, nil];
        [alert show];
        
#if !__has_feature(objc_arc)
        [alert release];
#endif
    });

}

#import <Availability.h>
#undef ah_retain
#undef ah_dealloc
#undef ah_autorelease autorelease
#undef ah_dealloc dealloc
#if __has_feature(objc_arc)
#define ah_retain self
#define ah_release self
#define ah_autorelease self
#define ah_dealloc self
#else
#define ah_retain retain
#define ah_release release
#define ah_autorelease autorelease
#define ah_dealloc dealloc
#undef __bridge
#define __bridge
#undef __bridge_transfer
#define __bridge_transfer
#endif
 
//  Weak reference support
 
#import <Availability.h>
#if !__has_feature(objc_arc_weak)
#undef ah_weak
#define ah_weak unsafe_unretained
#undef __ah_weak
#define __ah_weak __unsafe_unretained
#endif
 
//  Weak delegate support
 
#import <Availability.h>
#undef ah_weak_delegate
#undef __ah_weak_delegate
#if __has_feature(objc_arc_weak) && \
(!(defined __MAC_OS_X_VERSION_MIN_REQUIRED) || __MAC_OS_X_VERSION_MIN_REQUIRED >= __MAC_10_8)
#define ah_weak_delegate weak
#define __ah_weak_delegate __weak
#else
#define ah_weak_delegate unsafe_unretained
#define __ah_weak_delegate __unsafe_unretained
#endif