cocos2dx事件addEventListenerWithSceneGraphPriority方法

在官方文档中,node对象有一个_eventDispatcher成员变量,所以继承node的对象也有这个变量。

当我们需要去层等没有集成点击事件的节点监听点击事件时,需要这样,实例代码:

listener->onTouchBegan = [=](Touch* touch, Event* event){
    
    Vec2 locationInNode = this->convertToNodeSpace(touch->getLocation());
    Size s = this->getContentSize();
    Rect rect = Rect(0, 0, s.width, s.height);
    
    if (rect.containsPoint(locationInNode))
    {
        this->setColor(Color3B::RED);
        return true;
    }
    return false;
};

listener->onTouchEnded = [=](Touch* touch, Event* event){
    this->setColor(Color3B::WHITE);
    
    if (_removeListenerOnTouchEnded)
    {
        _eventDispatcher->removeEventListener(listener);
    }
};

if (_fixedPriority != 0)
{
    _eventDispatcher->addEventListenerWithFixedPriority(listener, _fixedPriority);
}
else
{
    _eventDispatcher->addEventListenerWithSceneGraphPriority(listener, this);
}

作为初学者,我刚看到这样的代码有点不懂,两个添加事件监听的方法,即:

addEventListenerWithFixedPriority和addEventListenerWithSceneGraphPriority。

于是官网上学习,发现后者可以实现当节点销毁时,同时销毁添加的事件监听。

前者官网上有相应的解释,但是不没有理解。后来学习了官网实例,才了解了addEventListenerWithFixedPriority的作用。所以学习还是要理论和实践相结合。

对于addEventListenerWithFixedPriority(EventListener* listener, int fixedPriority),需要传两个参数,一个是需要监听的事件,另一个是监听的事件等级,等级越小,事件越靠前

cocos2dx事件addEventListenerWithSceneGraphPriority方法_第1张图片

这个是官方示例,当我点击黄色和红色区域时,先收到点击事件的是红色图片。如下图:

cocos2dx事件addEventListenerWithSceneGraphPriority方法_第2张图片

因为给上面各个图片的点击事件中,蓝色的fixedPriority为30, 红色的fixedPriority为35,黄色的fixedPriority为40,所以,如果点击蓝色和红色的共同区域,先收到事件的是蓝色;点击红色和黄色的共同区域,先收到事件的是红色。

下面是实例代码:

// FixedPriorityChangedTest

class TouchableSprite : public Sprite
{
public:
    static TouchableSprite* create(int priority = 0)
    {
        auto ret = new (std::nothrow) TouchableSprite(priority);
        if (ret && ret->init())
        {
            ret->autorelease();
        }
        else
        {
            CC_SAFE_DELETE(ret);
        }
        return ret;
    }

protected:
    TouchableSprite(int priority)
    : _listener(nullptr)
    , _fixedPriority(priority)
    , _removeListenerOnTouchEnded(false)
    {
    }
    
public:
    void onEnter() override
    {
        Sprite::onEnter();
        
        auto listener = EventListenerTouchOneByOne::create();
        listener->setSwallowTouches(true);
        
        listener->onTouchBegan = [=](Touch* touch, Event* event){
            
            Vec2 locationInNode = this->convertToNodeSpace(touch->getLocation());
            Size s = this->getContentSize();
            Rect rect = Rect(0, 0, s.width, s.height);
            
            if (rect.containsPoint(locationInNode))
            {
                this->setColor(Color3B::RED);
                return true;
            }
            return false;
        };
        
        listener->onTouchEnded = [=](Touch* touch, Event* event){
            this->setColor(Color3B::WHITE);
            
            if (_removeListenerOnTouchEnded)
            {
                _eventDispatcher->removeEventListener(listener);
            }
        };
        
        if (_fixedPriority != 0)
        {
            _eventDispatcher->addEventListenerWithFixedPriority(listener, _fixedPriority);
        }
        else
        {
            _eventDispatcher->addEventListenerWithSceneGraphPriority(listener, this);
        }

        _listener = listener;
    }
    
    void onExit() override
    {
        _eventDispatcher->removeEventListener(_listener);
        
        Sprite::onExit();
    }

    void removeListenerOnTouchEnded(bool toRemove) { _removeListenerOnTouchEnded = toRemove; };
    
    inline EventListener* getListener() { return _listener; };
    
private:
    EventListener* _listener;
    int _fixedPriority;
    bool _removeListenerOnTouchEnded;
};

void FixedPriorityTest::onEnter()
{
    EventDispatcherTestDemo::onEnter();
    
    Vec2 origin = Director::getInstance()->getVisibleOrigin();
    Size size = Director::getInstance()->getVisibleSize();
    
    auto sprite1 = TouchableSprite::create(30);
    sprite1->setTexture("Images/CyanSquare.png");
    sprite1->setPosition(origin+Vec2(size.width/2, size.height/2) + Vec2(-80, 40));
    addChild(sprite1, 10);
    
    auto sprite2 = TouchableSprite::create(35);
    sprite2->setTexture("Images/MagentaSquare.png");
    sprite2->setPosition(origin+Vec2(size.width/2, size.height/2));
    addChild(sprite2, 20);
    
    auto sprite3 = TouchableSprite::create(40);
    sprite3->setTexture("Images/YellowSquare.png");
    sprite3->setPosition(Vec2(0, 0));
    sprite2->addChild(sprite3, 1);

}


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