有关quick-cocos2dx中的class方法的笔记

烁灵 posted @ 2014年8月12日 19:35 in Cocos2dx with tags init class quick-cocos2dx ctor 构造方法 , 10537 阅读

因为之前师父告诉咱ctor相当于构造函数,不熟悉lua模拟面向对象细节的咱用的时候感觉怪怪的,所以这里试着总结下,慢慢写。

首先看下源码:(function.lua)

function class(classname, super)
    local superType = type(super)
    local cls

    if superType ~= "function" and superType ~= "table" then
        superType = nil
        super = nil
    end

    if superType == "function" or (super and super.__ctype == 1) then
        -- inherited from native C++ Object
        cls = {}

        if superType == "table" then
            -- copy fields from super
            for k,v in pairs(super) do cls[k] = v end
            cls.__create = super.__create
            cls.super    = super
        else
            cls.__create = super
            cls.ctor = function() end
        end

        cls.__cname = classname
        cls.__ctype = 1

        function cls.new(...)
            local instance = cls.__create(...)
            -- copy fields from class to native object
            for k,v in pairs(cls) do instance[k] = v end
            instance.class = cls
            instance:ctor(...)
            return instance
        end

    else
        -- inherited from Lua Object
        if super then
            cls = {}
            setmetatable(cls, {__index = super})
            cls.super = super
        else
            cls = {ctor = function() end}
        end

        cls.__cname = classname
        cls.__ctype = 2 -- lua
        cls.__index = cls

        function cls.new(...)
            local instance = setmetatable({}, cls)
            instance.class = cls
            instance:ctor(...)
            return instance
        end
    end

    return cls
end

对于使用传入function方式继承cocos2dx类的自定义类如MainScene:(MainScene.lua)

local MainScene = class("MainScene", function()
    return display.newScene("MainScene")
end)

function会成为__create变量的值,在new方法中调用,返回值为display.newScene("MainScene"),即:(display.lua)

function display.newScene(name)
    local scene = CCScene:create()
    scene:setNodeEventEnabled(true)
    scene:setAutoCleanupEnabled()
    scene.name = name or "<unknown-scene>"
    return scene
end

CCScene:create()返回的对象,该对象由cocos2dx的工厂方法create创建,由cocos2dx的内存管理机制管理。

之后调用该对象的ctor方法,在官方demo中MainScene的ctor为自己添加了CCLabelTTF控件,这个在cocos2dx中更像是init方法的行为,而不是构造函数……

比较一下:(CCScene.cpp)

CCScene *CCScene::create()
{
    CCScene *pRet = new CCScene();
    if (pRet && pRet->init())
    {
        pRet->autorelease();
        return pRet;
    }
    else
    {
        CC_SAFE_DELETE(pRet);
        return NULL;
    }
}

而init方法做了控件等的初始化和附加等操作:(HelloWorld.cpp,注释略)

bool HelloWorld::init()
{
    if ( !CCLayer::init() )
    {
        return false;
    }
    
    CCSize visibleSize = CCDirector::sharedDirector()->getVisibleSize();
    CCPoint origin = CCDirector::sharedDirector()->getVisibleOrigin();
    CCMenuItemImage *pCloseItem = CCMenuItemImage::create(
                                        "CloseNormal.png",
                                        "CloseSelected.png",
                                        this,
                                        menu_selector(HelloWorld::menuCloseCallback));
    
    pCloseItem->setPosition(ccp(origin.x + visibleSize.width - pCloseItem->getContentSize().width/2 ,
                                origin.y + pCloseItem->getContentSize().height/2));
    CCMenu* pMenu = CCMenu::create(pCloseItem, NULL);
    pMenu->setPosition(CCPointZero);
    this->addChild(pMenu, 1);
    CCLabelTTF* pLabel = CCLabelTTF::create("Hello World", "Arial", TITLE_FONT_SIZE);
    pLabel->setPosition(ccp(origin.x + visibleSize.width/2,
                            origin.y + visibleSize.height - pLabel->getContentSize().height));
    this->addChild(pLabel, 1);
    CCSprite* pSprite = CCSprite::create("HelloWorld.png");
    pSprite->setPosition(ccp(visibleSize.width/2 + origin.x, visibleSize.height/2 + origin.y));
    this->addChild(pSprite, 0);
    
    return true;
}

c++中的new主要做了:

调用构造函数,调用init方法为scene\layer等添加控件,进入内存管理机制

lua中的此时的new主要做了:

调用原create方法进入内存管理机制,调用ctor方法为scene\layer等添加控件,同时可以用来初始化当前“对象”的“成员变量”

 

结论:

目前自己认为,这种场合ctor可以用来对当前“对象”的“成员变量”进行初始化,这个行为和构造函数相似;同时生成并附加给场景\层所需的控件,这个行为与init方法相似,同时做了两件事。需要自己注意的是ctor执行前,即初始化成员变量前,当前对象已经是(可以当做)由cocos2dx工厂方法create出来的参与了内存管理的对象了。

对于在cocos2dx中通过create来创建并使用的类/子类,在quick中可通过new来创建并使用。

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2022年8月18日 13:07

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