如何給類增加屬性CGRect的情況

@interface UIImageView(f)

@property (nonatomic,assign) CGRect validFrame;

@end

@implementation UIImageView(f)

static const void *VALID_FRAME_KEY = &VALID_FRAME_KEY;

@dynamic validFrame;

-(void)setValidFrame:(CGRect)frame{

    NSValue *rectValue = [NSValue valueWithCGRect:frame];

    objc_setAssociatedObject(self, VALID_FRAME_KEY, rectValue, OBJC_ASSOCIATION_ASSIGN);

}

-(CGRect)validFrame{

    NSValue *rectValue = objc_getAssociatedObject(self, VALID_FRAME_KEY);

    return [rectValue CGRectValue];

}

@end