編寫高質量OC代碼52建議總結：10.關聯對象

2019-11-09 15:27:57

字體：大中小

來源：轉載

供稿：網友

OBJC_EXPORT void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy) OBJC_EXPORT id objc_getAssociatedObject(id object, const void *key) OBJC_EXPORT void objc_removeAssociatedObjects(id object) 注意:

1.可以通過關聯對象機制把兩個對象連起來。

2.定義關聯對象時可指定內存管理語義，定義屬性時采用的“擁有關系”與“非擁有關系”。

3.只有在其他辦法都沒用的時候再引入關聯對象，這種做法通常會產生難以查找的BUG。

關聯策略

/**         *  OBJC_ASSOCIATION_ASSIGN              等價于@PRoperty (assign) ，                 @property (unsafe_unretained)            弱引用關聯對象                  *  OBJC_ASSOCIATION_RETAIN_NONATOMIC            等價于@property (strong, nonatomic)            強引用關聯對象，且為非原子操作                  *  OBJC_ASSOCIATION_COPY_NONATOMIC            等價于@property (copy, nonatomic)            復制關聯對象，且為非原子操作                           *  OBJC_ASSOCIATION_RETAIN            等價于@property (strong, atomic)            強引用關聯對象，且為原子操作                  *  OBJC_ASSOCIATION_COPY            等價于@property (copy, atomic)            復制關聯對象，且為原子操作                  其中，第 2 種與第 4 種、第 3 種與第 5 種關聯策略的唯一差別就在于操作是否具有原子性。         */        objc_setAssociatedObject(button, buttonKey, _imgView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
例：
1、倒入頭文件，聲明key:
#import <objc/runtime.h>char* const buttonKey = "buttonKey";2、設置關聯：
if (groupModel.isOpened) {        UIImageView * _imgView = [[UIImageView alloc]initWithFrame:CGRectMake(10, (44-16)/2, 14, 16)];        [_imgView setImage:[UIImage imageNamed:@"ico_list"]];        [sectionView addSubview:_imgView];        CGAffineTransform currentTransform = _imgView.transform;        CGAffineTransform newTransform = CGAffineTransformRotate(currentTransform, M_PI/2); // 在現在的基礎上旋轉指定角度        _imgView.transform = newTransform;        objc_setAssociatedObject(button, buttonKey, _imgView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);    }else{        UIImageView * _imgView = [[UIImageView alloc]initWithFrame:CGRectMake(10, (44-16)/2, 14, 16)];        [_imgView setImage:[UIImage imageNamed:@"ico_list"]];        [sectionView addSubview:_imgView];        objc_setAssociatedObject(button, buttonKey, _imgView, OBJC_ASSOCIATION_RETAIN_NONATOMIC);    }3、獲取關聯：
- (void)buttonPress:(UIButton *)sender//headButton點擊{    GroupModel *groupModel = dataSource[sender.tag];    UIImageView *imageView =  objc_getAssociatedObject(sender,buttonKey);    if (groupModel.isOpened) {            [UIView animateWithDuration:0.3 delay:0.0 options:UIViewAnimationOptionTransitionNone animations:^{                CGAffineTransform currentTransform = imageView.transform;                CGAffineTransform newTransform = CGAffineTransformRotate(currentTransform, -M_PI/2); // 在現在的基礎上旋轉指定角度                imageView.transform = newTransform;            } completion:^(BOOL finished) {                            }];                            }else{                    [UIView animateWithDuration:0.3 delay:0.0 options: UIViewAnimationOptionAllowUserInteraction |UIViewAnimationOptionCurveLinear animations:^{                CGAffineTransform currentTransform = imageView.transform;                CGAffineTransform newTransform = CGAffineTransformRotate(currentTransform, M_PI/2); // 在現在的基礎上旋轉指定角度                imageView.transform = newTransform;                        } completion:^(BOOL finished) {                            }];        }    groupModel.isOpened = !groupModel.isOpened;    [expandTable reloadSections:[NSIndexSet indexSetWithIndex:sender.tag] withRowAnimation:UITableViewRowAnimationAutomatic];}