CCDirector::sharedDirector()函数源码

static CCDisplayLinkDirector *s_SharedDirector = NULL;
CCDirector* CCDirector::sharedDirector(void)
{
    if (!s_SharedDirector)
    {
        s_SharedDirector = new CCDisplayLinkDirector();
        s_SharedDirector->init();
    }

    return s_SharedDirector;
}

类静态方法，获取全局唯一的 CCDirector 对象，如不存在则创建并获取对象