您好,登錄后才能下訂單哦!
這篇文章給大家介紹iOS中怎么關(guān)聯(lián)對(duì)象,內(nèi)容非常詳細(xì),感興趣的小伙伴們可以參考借鑒,希望對(duì)大家能有所幫助。
關(guān)聯(lián)對(duì)象源碼
存值
void objc_setAssociatedObject(id object, const void *key, id value, objc_AssociationPolicy policy) { _object_set_associative_reference(object, (void *)key, value, policy);}
我們調(diào)用此方法的時(shí)候,一共傳遞了四個(gè)參數(shù):
id object需要關(guān)聯(lián)的對(duì)象void *key對(duì)應(yīng)的keyid value對(duì)應(yīng)的值objc_AssociationPolicy policy內(nèi)存管理策略
內(nèi)存管理策略:
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. */};
對(duì)于四個(gè)參數(shù)理解完了之后讓我們看看它真正的實(shí)現(xiàn)函數(shù)_object_set_associative_reference
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); id new_value = value ? acquireValue(value, policy) : nil; { AssociationsManager manager; AssociationsHashMap &associations(manager.associations()); disguised_ptr_t disguised_object = DISGUISE(object);//得到對(duì)象地址 if (new_value) { // break any existing association. AssociationsHashMap::iterator i = associations.find(disguised_object);//首先通過(guò)對(duì)象的地址獲取對(duì)象的hashmap if (i != associations.end()) {//判斷是否已經(jīng)存在,已經(jīng)存在 // secondary table exists ObjectAssociationMap *refs = i->second;//取值,對(duì)應(yīng)的map ObjectAssociationMap::iterator j = refs->find(key);//通過(guò)key查找 if (j != refs->end()) {//如果已經(jīng)存在 old_association = j->second;//取到原來(lái)老的值,以便后邊對(duì)其釋放 j->second = ObjcAssociation(policy, new_value);//存儲(chǔ)新的值 } else {//不存在 (*refs)[key] = ObjcAssociation(policy, new_value); } } else {//如果不存在,創(chuàng)建一個(gè) // create the new association (first time). ObjectAssociationMap *refs = new ObjectAssociationMap; associations[disguised_object] = refs; (*refs)[key] = ObjcAssociation(policy, new_value); object->setHasAssociatedObjects(); } } else {//不存在則創(chuàng)建一個(gè) // setting the association to nil breaks the association. 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); } } } } // release the old value (outside of the lock). if (old_association.hasValue()) ReleaseValue()(old_association);}
通過(guò)以上代碼我們可以看出其實(shí)關(guān)聯(lián)對(duì)象在存儲(chǔ)的時(shí)候在,生成了一個(gè)AssociationsManager單例對(duì)象,所以應(yīng)用中所有的管理對(duì)象都存儲(chǔ)于此AssociationsManager中。
具體存儲(chǔ)的實(shí)現(xiàn)是借助了C++的關(guān)聯(lián)容器unordered_map實(shí)現(xiàn)的。具體可以參看代碼中我加的注釋。
整個(gè)過(guò)程就是通過(guò)object對(duì)象的地址存儲(chǔ)了一個(gè)類似hashmap的東西;取到此hashmap,然后通過(guò)鍵值對(duì)的方式將我們需要存儲(chǔ)的值存儲(chǔ)到此hashmap中,這個(gè)過(guò)程中如果有舊值,則最后會(huì)將舊值就行釋放
取值
取值的過(guò)程其實(shí)就比較簡(jiǎn)單了,就相當(dāng)于從一個(gè)hashmap中取值
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); 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;}
關(guān)于iOS中怎么關(guān)聯(lián)對(duì)象就分享到這里了,希望以上內(nèi)容可以對(duì)大家有一定的幫助,可以學(xué)到更多知識(shí)。如果覺(jué)得文章不錯(cuò),可以把它分享出去讓更多的人看到。
免責(zé)聲明:本站發(fā)布的內(nèi)容(圖片、視頻和文字)以原創(chuàng)、轉(zhuǎn)載和分享為主,文章觀點(diǎn)不代表本網(wǎng)站立場(chǎng),如果涉及侵權(quán)請(qǐng)聯(lián)系站長(zhǎng)郵箱:is@yisu.com進(jìn)行舉報(bào),并提供相關(guān)證據(jù),一經(jīng)查實(shí),將立刻刪除涉嫌侵權(quán)內(nèi)容。