[2]Cocos2d-x之引用计算(referenceCount)的增减时机

总结：
     1、当节点（节点指像Scene、Layer、Sprite等继承Node的子类）被创建时，引用计数（referenceCount）加1。
     2、当节点添加到父节点或执行动作时，没错执行动作也会加1，引用计数加1。
     3、当每一帧过后 AutoreleasePool会调用clear函数，将存放的ref的引用计数减1。这里的每一帧可以理解为每一个画面的切换。

测试代码基于cocos2d-x v3.3：
头文件：ActionTest.h

#ifndef __ACTIONTEST_H__
#define __ACTIONTEST_H__

#include "cocos2d.h"
#include <iostream>

USING_NS_CC;

class ActionTest :public Layer{
public:
CREATE_FUNC(ActionTest);

bool init();

private:
void moveByAndMoveTo();
Sprite* _pk1;
Sprite* _pk2;
};
#endif

实现类：ActionTest.cpp

#include "ActionTest.h"

bool ActionTest::init(){

auto s = Director::getInstance()->getWinSize();
_pk1 = Sprite::create("pk.png");	//创建节点，_pk1引用计数加1
CCLOG("pk1 ref count is %d", _pk1->getReferenceCount());
_pk1->setAnchorPoint(Vec2(0.5, 0.5));
_pk1->setPosition(Vec2(s.width/2, s.height/2));
_pk1->retain();		//调用retain()，_pk1引用计数加1
CCLOG("pk1 ref count is %d", _pk1->getReferenceCount());

auto moveByAndMoveToItem = MenuItemFont::create("moveByAndMoveToTest",CC_CALLBACK_0(ActionTest::moveByAndMoveTo,this));

auto menu = Menu::create(moveByAndMoveToItem,nullptr);
menu->alignItemsVertically();
addChild(menu);

return true;

}

void ActionTest::moveByAndMoveTo(){
auto s = Director::getInstance()->getWinSize();
auto scene = Scene::create();
auto layer = Layer::create();

_pk2 = Sprite::create("pk.png");
_pk2->setColor(Color3B::GREEN);
_pk2->setPosition(Vec2(s.width, s.height / 2));
//创建Node，_pk2引用加一
CCLOG("pk2 ref count is %d", _pk1->getReferenceCount());
CCLOG("pk1 ref count is %d", _pk1->getReferenceCount());
scene->addChild(layer);
layer->addChild(_pk1);
layer->addChild(_pk2);
//添加到父类,_pk2,_pk1引用加一
CCLOG("pk2add ref count is %d", _pk1->getReferenceCount());
CCLOG("pk1add ref count is %d", _pk1->getReferenceCount());

//MoveBy是向量改变值,沿着向量路径运动
auto mBy = MoveBy::create(3,Vec2(s.width/2,s.height/2));

//MoveTo是移动到特定点
auto mTo = MoveTo::create(3, Vec2(s.width / 2, s.height / 2));
_pk1->runAction(mTo);
_pk2->runAction(mBy);
//执行动作引用加一
CCLOG("pk2action ref count is %d", _pk1->getReferenceCount());
CCLOG("pk1action ref count is %d", _pk1->getReferenceCount());
Director::getInstance()->pushScene(scene);
}

注意：在init方法中调用retain方法，是因为调用init时_pk1的创建引用计数加一，但是其它类再引用_pk1时，引用数会变为0，因为autoreleasepool的cleae将引用计数减1，要再调用retain保持引用数大于0，不然会出现异常 "reference
count should greater than 0"