objc Runtime 关联对象为什么不走 set 方法？

@interface UIView (Rotate ) @property (nonatomic, strong ) NSString * animating; - (void ) startSpin; - (void ) stopSpin; @end //-------------------------------------------- #import "UIView+Rotate.h" #import <objc/runtime.h> #define ANIMATING_TAG @"1" #define ANIMATING_STOP_TAG @"0" @implementation UIView (Rotate ) static void * mAnimating = &mAnimating; -(NSString *)animating{ return objc_getAssociatedObject (self,mAnimating ); } -(void )setAnimating:(NSString *)aAnimating { objc_setAssociatedObject (self, mAnimating, aAnimating, OBJC_ASSOCIATION_RETAIN_NONATOMIC ); } - (void ) spinWithOptions: (UIViewAnimationOptions ) options{ [UIView animateWithDuration: 0.5f delay: 0.0f options: options animations: ^{ self.transform = CGAffineTransformRotate (self.transform, M_PI / 2 ); } completion: ^(BOOL finished ) { if (finished ) { if ([self checkIsAnimating]) { // if flag still set, keep spinning with constant speed [self spinWithOptions: UIViewAnimationOptionCurveLinear]; } else if (options != UIViewAnimationOptionCurveEaseOut ) { // one last spin, with deceleration [self spinWithOptions: UIViewAnimationOptionCurveEaseOut]; } } }]; } - (void ) startSpin{ if (![self checkIsAnimating]) { [self setAnimating:ANIMATING_TAG]; [self spinWithOptions: UIViewAnimationOptionCurveEaseIn]; } } - (void ) stopSpin { [self setAnimating:ANIMATING_STOP_TAG]; } - (BOOL )checkIsAnimating{ if (!self.animating ) { return NO; } if ([self.animating isEqualToString:ANIMATING_TAG]) { return YES; }else{ return NO; } } @end