为什么通过如下代码获取到的contentSize为0？
bool MCCCaterpillarSprite::init()
{
if (!Node::init()) {
return false;
}
this->m_rootNode = CSLoader::createNode("Node/Caterpillar.csb");
this->m_actionTimeline = CSLoader::createTimeline("Node/Caterpillar.csb");
this->m_isPause = false;
CCLOG("1111");
toolsInstance->readRect(this->m_rootNode->getBoundingBox());
this->setContentSize(this->m_rootNode->getContentSize());
this->addChild(m_rootNode);
this->m_rootNode->runAction(this->m_actionTimeline);
return true;
}