http://blog.youkuaiyun.com/tonny_guan/article/details/38149367
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。
提示 在Lambda表达式中[]表示接下来开始定义Lambda函数,[]之后的()是Lambda函数的参数列表,{}中间就是函数体。
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。