OC runtime学习笔记之关联对象

/// 对象关联策略
typedef OBJC_ENUM(uintptr_t, objc_AssociationPolicy) {
 OBJC_ASSOCIATION_ASSIGN = 0,  
 OBJC_ASSOCIATION_RETaiN_NONATOMIC = 1, 
 OBJC_ASSOCIATION_COPY_NONATOMIC = 3, 
 OBJC_ASSOCIATION_RETAIN = 01401, 
 OBJC_ASSOCIATION_COPY = 01403  
};


void objc_setAssociatedObject(id object, const void * key, id value, objc_AssociationPolicy policy);


id objc_getAssociatedObject(id object, const void * key);


void objc_removeAssociatedObjects(id object)；

static const void * _Nonnull titleKey = @"titleKey";

- (void)setTitle:(NSString *)title
{
 objc_setAssociatedObject(self, titleKey, key, OBJC_ASSOCIATION_RETAIN);
}

- (NSString *)title
{
 return objc_getAssociatedObject(self, titleKey);
}

/// 方法为我加过注释的代码。
void _object_set_associative_reference(id object, void *key, id value, uintptr_t policy) {
 
 // 取原来的绑定关系，新绑定关系原来关系为空
 ObjcAssociation old_association(0, nil);
 // 验证参数
 id new_value = value ? acquireValue(value, policy) : nil;
 {
 // 内部绑定关系管理器.内部管理一个全局 AssociationsHashMap
 AssociationsManager manager;
 // 管理器中的绑定关系Map
 AssociationsHashMap &associations(manager.associations());
 // 生成伪装地址。处理参数 object 地址
 disguised_ptr_t disguised_object = DISGUISE(object);
 if (new_value) {
  // 打破原来存在的绑定关系
  AssociationsHashMap::iterator i = associations.find(disguised_object); // 以伪装地址为key 在AssociationsHashMap找objc 对应的二级 Map
  if (i != associations.end()) {
  // 二级Map存在。并取二级map： ObjectAssociationMap
  ObjectAssociationMap *refs = i->second;
  // 同样的方法找到 ObjectAssociationMap 中绑定关系
  ObjectAssociationMap::iterator j = refs->find(key); // 通过key 在ObjectAssociationMap 中找ObjcAssociation
  if (j != refs->end()) {
   // 找到原来 ObjcAssociation 关系，直接赋值old_association
   old_association = j->second;
   j->second = ObjcAssociation(policy, new_value);
  } else {
   // 不存在 -> 重新创建一次
   (*refs)[key] = ObjcAssociation(policy, new_value);
  }
  } else {
  // 不存在二级Map 就直接从新创建
  ObjectAssociationMap *refs = new ObjectAssociationMap;
  associations[disguised_object] = refs;
  (*refs)[key] = ObjcAssociation(policy, new_value);
  object->setHasAssociatedObjects();
  }
 } else {
  // 未传 value ，直接设置关联关系为nil。移除原来的绑定关系
  AssociationsHashMap::iterator i = associations.find(disguised_object);
  if (i != associations.end()) {
  ObjectAssociationMap *refs = i->second;
  ObjectAssociationMap::iterator j = refs->find(key);
  if (j != refs->end()) {
   old_association = j->second;
   refs->erase(j);
  }
  }
 }
 }
 // 释放 old value.
 if (old_association.hasValue()) ReleaseValue()(old_association);
}