在Cocos2d-x 3.0之后提供了对C++11标准[1]的支持，其中的Lambda[2]表达式使用起来非常简洁。我们可以使用Lambda表达式重构上一节的实例。

我们可以将下面的代码：

listener->onTouchBegan =CC_CALLBACK_2(HelloWorld::onTouchBegan, this);
... ...
bool HelloWorld::onTouchBegan(Touch*touch, Event* event) {
    ......
    returnfalse;
}

替换为如下代码：

listener->onTouchBegan = [](Touch*touch, Event* event){
   ... ...
   return false;
};

上面的语句[](Touch* touch, Event* event){ …}就是Lambda表达式。Lambda表达式就是JavaScript语言中的匿名函数，Java中的匿名内部类，就是在表达式中直接声明函数，而不是独立声明函数。

重构之后的HelloWorldScene.cpp主要修改的代码如下：

void HelloWorld::onEnter()
{
    Layer::onEnter();
    log("HelloWorldonEnter");
   
   auto listener = EventListenerTouchOneByOne::create();
   listener->setSwallowTouches(true);
   
   listener->onTouchBegan = [](Touch* touch, Event* event){                                                      ①         
       auto target = static_cast<Sprite*>(event->getCurrentTarget());
             PointlocationInNode = target->convertToNodeSpace(touch->getLocation());
       Size s = target->getContentSize();
       Rect rect = Rect(0, 0, s.width, s.height);
 
       if (rect.containsPoint(locationInNode))
       {
            log("sprite x = %f, y = %f", locationInNode.x, locationInNode.y);
                       log("spritetag = %d", target->getTag());
                      target->runAction(ScaleBy::create(0.06f,1.06f));
            return true;
       }
       return false;
   };
   
   listener->onTouchMoved = [](Touch* touch, Event* event){                                                      ②
       auto target = static_cast<Sprite*>(event->getCurrentTarget());
       // 移动当前按钮精灵的坐标位置
       target->setPosition(target->getPosition() + touch->getDelta());
   };
 
   listener->onTouchEnded = [](Touch* touch, Event* event){                                                      ③
       auto target = static_cast<Sprite*>(event->getCurrentTarget());
       log("sprite onTouchesEnded.. ");
 
                PointlocationInNode = target->convertToNodeSpace(touch->getLocation());
       Size s = target->getContentSize();
       Rect rect = Rect(0, 0, s.width, s.height);
      
       if (rect.containsPoint(locationInNode))
       {
            log("sprite x = %f, y = %f", locationInNode.x, locationInNode.y);
                      log("sprite tag = %d",target->getTag());
                      target->runAction(ScaleTo::create(0.06f,1.0f));
       }
   };
 
    //添加监听器
    EventDispatcher*eventDispatcher = Director::getInstance()->getEventDispatcher();
    eventDispatcher->addEventListenerWithSceneGraphPriority(listener,
                                                                                     getChildByTag(kBoxA_Tag));
    eventDispatcher->addEventListenerWithSceneGraphPriority(listener->clone(),
                                                                                     getChildByTag(kBoxB_Tag));
    eventDispatcher->addEventListenerWithSceneGraphPriority(listener->clone(),
                                                                                     getChildByTag(kBoxC_Tag));
}

上述代码第①、②、③行分别使用了Lambda表达式定义的匿名函数，具体代码不用再解释。从上面代码看使用Lambda表达式非常简洁，由于不需要单独定义回调函数，对应的头文件代码也比较简洁，HelloWorldScene.h主要代码如下：

class HelloWorld : public cocos2d::Layer
{
public:
   static cocos2d::Scene* createScene();
  virtual bool init(); 
    virtualvoid onEnter();
    virtualvoid onExit();
   
   CREATE_FUNC(HelloWorld);
};

除了触摸事件还有键盘事件、鼠标事件、加速度事件和自定义事件等也都可以使用Lambda表达式。

Cocos2d-x开发实例：使用Lambda 表达式