cocos的cclayer有onEnter()方法，這個在啥時候執行啊？

void CCNode::addChild(CCNode *child, int zOrder, int tag)
{	
	CCAssert( child != NULL, "Argument must be non-nil");
	CCAssert( child->m_pParent == NULL, "child already added. It can't be added again");

	if( ! m_pChildren )
	{
		this->childrenAlloc();
	}

	this->insertChild(child, zOrder);

	child->m_nTag = tag;

	child->setParent(this);

	if( m_bIsRunning )
	{
		child->onEnter();
		child->onEnterTransitionDidFinish();
	}
}

看了代碼就一目瞭然，然來只要加載他的對象在跑，那他就立即執行