之前了解了分类的编译与运行和一些知识，其中提到分类不能直接加属性，今天就来看看分类怎么添加属性的，直接看例子：
#import <objc/runtime.h>
@implementation Person (Test)
- (void)setName:(NSString*)name{
objc_setAssociatedObject(self, @"NameKey", name, OBJC_ASSOCIATION_COPY_NONATOMIC);
}
- (NSString*)name{
return objc_getAssociatedObject(self, @"NameKey");
}
@end
-
设置
- 从objc4-750源码探究，先来看设置：
//通过 key : value 的形式给对象 object 设置关联属性
void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy) {
_object_set_associative_reference(object, (void *)key, value, policy);
}
void _object_set_associative_reference(id object, void *key, id value, uintptr_t policy) {
// retain the new value (if any) outside the lock.
ObjcAssociation old_association(0, nil);//每个关联属性的键值队----值和策略
id new_value = value ? acquireValue(value, policy) : nil;//进行内存管理
{
AssociationsManager manager;//管理所有关联的属性的类，全局的
AssociationsHashMap &associations(manager.associations());//初始化 HashMap
disguised_ptr_t disguised_object = DISGUISE(object);//当前对象的地址按位取反后作为key
if (new_value) {
// break any existing association.
AssociationsHashMap::iterator i = associations.find(disguised_object);//<fisrt : disguised_object , second : ObjectAssociationMap> 类似于元组，存着所有关联属性的键值对
if (i != associations.end()) {
// secondary table exists
ObjectAssociationMap *refs = i->second;//一个对象的所有关联属性键值对
ObjectAssociationMap::iterator j = refs->find(key);//<fisrt : 标识（自定义的） , second : ObjcAssociation>
if (j != refs->end()) {
old_association = j->second;//新值覆盖
j->second = ObjcAssociation(policy, new_value);//ObjcAssociation存放关联属性
} else {
(*refs)[key] = ObjcAssociation(policy, new_value);
}
} else {
// create the new association (first time).
ObjectAssociationMap *refs = new ObjectAssociationMap;
associations[disguised_object] = refs;
(*refs)[key] = ObjcAssociation(policy, new_value);
object->setHasAssociatedObjects();//设置当前的isa指针
}
} else { ... }
}
// release the old value (outside of the lock).
if (old_association.hasValue()) ReleaseValue()(old_association);
}
AssociationsManager里存着AssciationsHashMap，
AssciationsHashMap里存着<fisrt : disguised_ptr_t , second : ObjectAssociationMap>，
ObjectAssociationMap里存着<fisrt : 标识（自定义的） , second : ObjcAssociation>，
ObjcAssociation里存着策略policy和值value。
所以最终关联属性就是存放在ObjcAssociation里。
-
获取
- 然后获取自然也是从
ObjcAssociation类里获取：
//通过 key 获取关联的属性 object
id objc_getAssociatedObject(id object, const void *key) {
return _object_get_associative_reference(object, (void *)key);
}
id _object_get_associative_reference(id object, void *key) {
id value = nil;
uintptr_t policy = OBJC_ASSOCIATION_ASSIGN;
{
AssociationsManager manager;
AssociationsHashMap &associations(manager.associations());
disguised_ptr_t disguised_object = DISGUISE(object);
AssociationsHashMap::iterator i = associations.find(disguised_object);//取出
if (i != associations.end()) {
ObjectAssociationMap *refs = i->second;
ObjectAssociationMap::iterator j = refs->find(key);
if (j != refs->end()) {
ObjcAssociation &entry = j->second;
value = entry.value();
policy = entry.policy();
if (policy & OBJC_ASSOCIATION_GETTER_RETAIN) {
objc_retain(value);
}
}
}
}
if (value && (policy & OBJC_ASSOCIATION_GETTER_AUTORELEASE)) {
objc_autorelease(value);
}
return value;
}
-
销毁
- 当对象销毁时，关联属性也随之销毁：
- (void)dealloc {
_objc_rootDealloc(self);
}
void
_objc_rootDealloc(id obj)
{
assert(obj);
obj->rootDealloc();
}
inline void
objc_object::rootDealloc()
{
if (isTaggedPointer()) return; // fixme necessary?
if (fastpath(isa.nonpointer &&
!isa.weakly_referenced &&
!isa.has_assoc &&
!isa.has_cxx_dtor &&
!isa.has_sidetable_rc))
{
assert(!sidetable_present());
free(this);
}
else {
object_dispose((id)this);//有关联对象时走这
}
}
id
object_dispose(id obj)
{
if (!obj) return nil;
objc_destructInstance(obj);
free(obj);
return nil;
}
void *objc_destructInstance(id obj)
{
if (obj) {
// Read all of the flags at once for performance.
bool cxx = obj->hasCxxDtor();
bool assoc = obj->hasAssociatedObjects();
// This order is important.
if (cxx) object_cxxDestruct(obj);
if (assoc) _object_remove_assocations(obj);//移除关联属性
obj->clearDeallocating();
}
return obj;
}
void _object_remove_assocations(id object) {
vector< ObjcAssociation,ObjcAllocator<ObjcAssociation> > elements;
{
AssociationsManager manager;
AssociationsHashMap &associations(manager.associations());
if (associations.size() == 0) return;
disguised_ptr_t disguised_object = DISGUISE(object);//key
AssociationsHashMap::iterator i = associations.find(disguised_object);
if (i != associations.end()) {
// copy all of the associations that need to be removed.
ObjectAssociationMap *refs = i->second;
for (ObjectAssociationMap::iterator j = refs->begin(), end = refs->end(); j != end; ++j) {
elements.push_back(j->second);
}
// remove the secondary table.
delete refs;
associations.erase(i);
}
}
// the calls to releaseValue() happen outside of the lock.
for_each(elements.begin(), elements.end(), ReleaseValue());//移除
}
- 当然也可以手动移除：
//移除对象所关联的属性
void objc_removeAssociatedObjects(id object)
{
if (object && object->hasAssociatedObjects()) {
_object_remove_assocations(object);
}
}
分类关联属性其实就是利用它的
AssociationsManager管理保存在ObjcAssociation里的关联属性。
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