Cocos2dx Game Development Study Notes 3-lua Object-Oriented Analysis

In Lua, metadata tables can be used to implement classes, objects, and inheritance. Methods related to meta-tables include setretriable (), _ index, getretriable (), and _ newindex.

I will not elaborate on the details of the meta-table here. I will introduce it a lot on the Internet. Here I will focus on the sections associated with cocos2dx.

In the LUA-binding library, extern. Lua has the following methods:

--Create an class.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        end        cls.ctor    = function() 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 = clone(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 clsend

Through this method, we can easily define a class and inherit a class.

Define a class:

MyClass = class("MyClass")function MyClass:ctor()print("MyClass:ctor()")endlocal myclass = MyClass:new()

Inherit a class:

GameLayer = class("GameLayer", function()local layer = cc.Layer:create()return layerend)local gamelayer = GameLayer:new()addChild(gamelayer)