iOS 关联对象(Associated Object)

1、category需要添加属性，可以使用关联对象来扩展对象

objc_setAssociatedObject(id _Nonnull object, const void * _Nonnull key,
                         id _Nullable value, objc_AssociationPolicy policy)
objc_getAssociatedObject(id _Nonnull object, const void * _Nonnull key)
objc_removeAssociatedObjects(id _Nonnull object)

id object  被关联的对象

const void *key  关联的key，唯一

id value  关联的对象

objc_AssociationPolicy policy  内存管理的策略

remove  移除一个管理对象

@property (nonatomic, copy) NSString *cid;
- (void)setCid:(NSString *)cid
{
    objc_setAssociatedObject(self, &kStringKey, cid, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
- (NSString *)cid
{
    return objc_getAssociatedObject(self, &kStringKey);
}

2、为UIButton类别添加点击block

// UIButton+Block.h
typedef void (^ButtonBlock)(id sender);
- (void)handleWithBlock:(ButtonBlock)block;
// UIButton+Block.m
static const char kButtonKey;
- (void)handleWithBlock:(ButtonBlock)block
{
    if (block)
    {
//        objc_setAssociatedObject(self, @selector(btnAction:), block, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        objc_setAssociatedObject(self, &kButtonKey, block, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
    }
    [self addTarget:self action:@selector(btnAction:) forControlEvents:UIControlEventTouchUpInside];
}
- (void)btnAction:(id)sender
{
//    ButtonBlock block = objc_getAssociatedObject(self, @selector(btnAction:));
    ButtonBlock block = objc_getAssociatedObject(self, &kButtonKey);
    if (block)
    {
        block(sender);
    }
}