Webkit的自訂屬性擷取函數以及屬性刪除函數實現

標籤：

概述: [CustomEnumerateProperty] 當給定的介面被枚舉時，允許你為指定介面的屬性擷取函數編寫自己的實現. 同樣，當介面的屬性被刪除時，[CustomDeleteProperty]允許你編寫自己的實現.

customEnumerateProperty](i), [CustomDeleteProperty](i)

用法: 這兩個修飾可作用在interface，用法如下:

    [        CustomEnumerateProperty,        CustomDeleteProperty    ] interface DataTransferItemList {    };

• [CustomEnumerateProperty] in JavaScriptCore: 你能編寫DataTransferItemList的屬性擷取函數，具體來說，你可以編寫這個函數JSXXX::getOwnPropertyNames(...)， 它來自於WebCore/bindings/js/JSDataTransferItemListCustom.cpp:

 void JSDataTransferItemList::getOwnPropertyNames(JSObject* object, ExecState* exec, PropertyNameArray& propertyNames, EnumerationMode mode){    JSDataTransferItemList* thisObject = jsCast<JSDataTransferItemList*>(object);    ASSERT_GC_OBJECT_INHERITS(thisObject, &s_info);    for (unsigned i = 0; i < static_cast<DataTransferItemList*>(thisObject->impl())->length(); ++i)        propertyNames.add(Identifier::from(exec, i));     Base::getOwnPropertyNames(thisObject, exec, propertyNames, mode);}

    [        CustomDeleteProperty    ] interface Storage {    };

• [CustomDeleteProperty] : 當Storage的屬性被刪除時，我們可以編寫自己的屬性刪除函數，具體點說，就是像這樣子編寫JSStorage::deleteProperty(...) 函數，它位於WebCore/bindings/js/JSStorageCustom.cpp:

bool JSStorage::deleteProperty(JSCell* cell, ExecState* exec, PropertyName propertyName){    JSStorage* thisObject = jsCast<JSStorage*>(cell);    // Only perform the custom delete if the object doesn‘t have a native property by this name.    // Since hasProperty() would end up calling canGetItemsForName() and be fooled, we need to check    // the native property slots manually.    PropertySlot slot;    if (getStaticValueSlot<JSStorage, Base>(exec, s_info.propHashTable(exec), thisObject, propertyName, slot))        return false;            JSValue prototype = thisObject->prototype();    if (prototype.isObject() && asObject(prototype)->hasProperty(exec, propertyName))        return false;    thisObject->m_impl->removeItem(propertyNameToString(propertyName));    return true;}

參考:1 http://trac.webkit.org/wiki/WebKitIDL#CustomEnumerateProperty2 souce code of webkit

Webkit的自訂屬性擷取函數以及屬性刪除函數實現