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从源码中也看到，如CCLayer::onEnter()中注册触摸事件，那么CCNode的onEnter函数是在什么时候调用的呢？下面从源码角度分析下：    /**      * Adds a child to the container with z order and tag     *     * If the child is added to a 'running' node, then 'onEnter' and 'onEnterTransitionDidFinish' will be called immediately.     *     * @param child     A child node     * @param zOrder    Z order for drawing priority. Please refer to setZOrder(int)     * @param tag       A interger to identify the node easily. Please refer to setTag(int)     */     //看上面的注释就可以清楚的知道，当我们当前的Node处于running时，那么添加到其上的     //子Node，会立即执行onEnter和onEnterTransitionDidFinish    virtual void addChild(CCNode* child, int zOrder, int tag);-->>void CCNode::addChild(CCNode *child, int zOrder, int tag){   .....    if( m_bRunning )    {        child->onEnter();        child->onEnterTransitionDidFinish();    }}    假如我们有三级Node，第三级加到第二级上时，第二级还没有处于'running'状态，那就意味着我们的    我们的第三级Node的onEnter函数没有被执行，那么在什么时候执行呢？        void CCNode::onEnter(){    //fix setTouchEnabled not take effect when called the function in onEnter in JSBinding.    m_bRunning = true;    if (m_eScriptType != kScriptTypeNone)    {        CCScriptEngineManager::sharedManager()->getScriptEngine()->executeNodeEvent(this, kCCNodeOnEnter);    }    //Judge the running state for prevent called onEnter method more than once,it's possible that this function called by addChild      if (m_pChildren && m_pChildren->count() > 0)    {        CCObject* child;        CCNode* node;        CCARRAY_FOREACH(m_pChildren, child)        {            node = (CCNode*)child;            if (!node->isRunning())            {                node->onEnter(); //循环遍历子Node，执行所有子Node的onEnter方法，我们的UI树一定会		                 //加入到一个处于'running'状态的Node，因为我们必然会至少有一个处于'running'				 状态的Node，即使是sceen，所以上面的第三级Node的OnEnter函数				 //会在第二级Node加入到第一级Node是执行(假设第一级Node处于'running'状态)。            }                    }    }    this->resumeSchedulerAndActions();   }

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