runtime笔记 之 动态给分类添加属性

Demo参考自这位大神的Github，小伙伴也可以参考他的例子。
先看例子

#import <UIKit/UIKit.h>

typedef void(^GestrueBlock)(id gestrueRecognize);
@interface UIGestureRecognizer (Block)

+ (instancetype)recognizeWithAction:(GestrueBlock)gestrueBlock;

@end


#import "UIGestureRecognizer+Block.h"
#import <objc/runtime.h>

static const int targetKey;

@implementation UIGestureRecognizer (Block)

+ (instancetype)recognizeWithAction:(GestrueBlock)gestrueBlock{
    __weak typeof(self) weakSelf = self;
    return [[weakSelf alloc]initWithActon:gestrueBlock];
}

- (instancetype)initWithActon:(GestrueBlock)gestrueBlock{
    self = [self init];
    [self addActonWithBlock:gestrueBlock];
    [self addTarget:self action:@selector(invoke:)];
    return self;
}

- (void)addActonWithBlock:(GestrueBlock)block{
    //第一步，设置关联对象
    if (block) {
        objc_setAssociatedObject(self, &targetKey, block, OBJC_ASSOCIATION_COPY);
    }
}

- (void)invoke:(id)sender{
    //取出关联对象
    GestrueBlock block = objc_getAssociatedObject(self, &targetKey);
    if (block) {
        block(sender);
    }
}

- (void)viewDidLoad {
    [super viewDidLoad];
    [self.view addGestureRecognizer:[UITapGestureRecognizer recognizeWithAction:^(id gestrueRecognize) {
        NSLog(@"点击了 self.view");
    }]];
}

由这篇文章中可以知道，我们通过分类的方法没法直接添加属性。所以可以通过关联对象的方式间接给分类添加属性。

---

下面开始介绍关联对象的几个方法：

关联对象

/** 
 * 使用给定的键和关联策略为给定对象设置关联值。
 * 
 * @param object 关联的源对象。
 * @param key 关联的键
 * @param value 关联的源对象所需要关联的值，通过nil来清除现有的关联。 
 * @param policy 关联策略
 * 
 * @see objc_setAssociatedObject
 * @see objc_removeAssociatedObjects
 */
void objc_setAssociatedObject(id _Nonnull object,
                              const void * _Nonnull key,
                              id _Nullable value, 
                              objc_AssociationPolicy policy);

关联策略

/**
 * Policies related to associative references.
 * These are options to objc_setAssociatedObject()
 */
typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
    OBJC_ASSOCIATION_ASSIGN = 0,           /**< Specifies a weak reference to the associated object. */
    OBJC_ASSOCIATION_RETAIN_NONATOMIC = 1, /**< Specifies a strong reference to the associated object. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_COPY_NONATOMIC = 3,   /**< Specifies that the associated object is copied. 
                                            *   The association is not made atomically. */
    OBJC_ASSOCIATION_RETAIN = 01401,       /**< Specifies a strong reference to the associated object.
                                            *   The association is made atomically. */
    OBJC_ASSOCIATION_COPY = 01403          /**< Specifies that the associated object is copied.
                                            *   The association is made atomically. */
};

获取关联对象

/** 
 * 获取关联源对象下给定的 key 所对应的值
 * 
 * @param object The source object for the association.
 * @param key The key for the association.
 * 
 * @return The value associated with the key \e key for \e object.
 * 
 * @see objc_setAssociatedObject
 */
id _Nullable objc_getAssociatedObject(id _Nonnull object, const void * _Nonnull key);

移除关联对象

/** 
 * 删除给定对象的所有关联。
 * 
 * @param object 关联的源对象
 * 
 * @note 
 *这个函数的主要目的是使对象返回到“原始状态”变得容易，
 *你不应该使用这个函数去除对象中的关联，
 *因为它还可以去除其他客户端可能添加到对象的关联。
 *通常你应该使用\ c objc_setAssociatedObject和一个nil值来清除关联。
 * 
 * @see objc_setAssociatedObject
 * @see objc_getAssociatedObject
 */
void objc_removeAssociatedObjects(id _Nonnull object);