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Cocos-2dx学习笔记(四) HelloWorld场景类

类定义原型如下:

#ifndef __HELLOWORLD_SCENE_H__#define __HELLOWORLD_SCENE_H__#include "cocos2d.h"class HelloWorld : public cocos2d::Layer{public:    // there‘s no ‘id‘ in cpp, so we recommend returning the class instance pointer    static cocos2d::Scene* createScene();    // Here‘s a difference. Method ‘init‘ in cocos2d-x returns bool, instead of returning ‘id‘ in cocos2d-iphone    virtual bool init();        // a selector callback    void menuCloseCallback(cocos2d::Ref* pSender);        // implement the "static create()" method manually    CREATE_FUNC(HelloWorld);};#endif // __HELLOWORLD_SCENE_H__

由以上代码可知,该类继承于Layer类。

1. static cocos2d::Scene* createScene();

在3.0版本后,该方法的名字已经发生了改变。该方法的作用是创建一个场景,并将该类的实例添加到场景中。

Scene* HelloWorld::createScene(){    // ‘scene‘ is an autorelease object    auto scene = Scene::create();        // ‘layer‘ is an autorelease object    auto layer = HelloWorld::create();    // add layer as a child to scene    scene->addChild(layer);    // return the scene    return scene;}

2. virtual bool init();

 改方法的作用有三:1、初始化父类;2、增加退出菜单;3、创建一个精灵,显示字符。

// on "init" you need to initialize your instancebool HelloWorld::init(){    //////////////////////////////    // 1. super init first    if ( !Layer::init() )    {        return false;    }        Size visibleSize = Director::getInstance()->getVisibleSize();    Vec2 origin = Director::getInstance()->getVisibleOrigin();    /////////////////////////////    // 2. add a menu item with "X" image, which is clicked to quit the program    //    you may modify it.    // add a "close" icon to exit the progress. it‘s an autorelease object    auto closeItem = MenuItemImage::create(                                           "CloseNormal.png",                                           "CloseSelected.png",                                           CC_CALLBACK_1(HelloWorld::menuCloseCallback, this));        closeItem->setPosition(Vec2(origin.x + visibleSize.width - closeItem->getContentSize().width/2 ,                                origin.y + closeItem->getContentSize().height/2));    // create menu, it‘s an autorelease object    auto menu = Menu::create(closeItem, NULL);    menu->setPosition(Vec2::ZERO);    this->addChild(menu, 1);    /////////////////////////////    // 3. add your codes below...    // add a label shows "Hello World"    // create and initialize a label        auto label = Label::createWithTTF("Hello World", "fonts/Marker Felt.ttf", 24);        // position the label on the center of the screen    label->setPosition(Vec2(origin.x + visibleSize.width/2,                            origin.y + visibleSize.height - label->getContentSize().height));    // add the label as a child to this layer    this->addChild(label, 1);    // add "HelloWorld" splash screen"    auto sprite = Sprite::create("HelloWorld.png");    // position the sprite on the center of the screen    sprite->setPosition(Vec2(visibleSize.width/2 + origin.x, visibleSize.height/2 + origin.y));    // add the sprite as a child to this layer    this->addChild(sprite, 0);        return true;}

3. void menuCloseCallback(cocos2d::Ref* pSender);

菜单回调函数在点击菜单项的时候调用,这里的作用退出应用。

void HelloWorld::menuCloseCallback(Ref* pSender){#if (CC_TARGET_PLATFORM == CC_PLATFORM_WP8) || (CC_TARGET_PLATFORM == CC_PLATFORM_WINRT)    MessageBox("You pressed the close button. Windows Store Apps do not implement a close button.","Alert");    return;#endif    Director::getInstance()->end();#if (CC_TARGET_PLATFORM == CC_PLATFORM_IOS)    exit(0);#endif}

4. CREATE_FUNC(HelloWorld);

这是一个宏,定义静态方法create(),用于创建一个自动回收的HelloWorld对象,该方法在createScene()中被调用,方法体如下:

#define CREATE_FUNC(__TYPE__) static __TYPE__* create() {     __TYPE__ *pRet = new __TYPE__();     if (pRet && pRet->init())     {         pRet->autorelease();         return pRet;     }     else     {         delete pRet;         pRet = NULL;         return NULL;     } }

 

Cocos-2dx学习笔记(四) HelloWorld场景类