Lua OOP class 的多个实例被忽略，为什么？

Question

I have a class called "Edit"

function Edit:new(x,y,w,h,text,fnt)
    o = {}
    setmetatable(o,EditMt)
    self.__index = self
    self.x = x or 0
    self.y = y or 0
    self.width = w or 10
    self.height = h or 10
    self.text = text or ""
    self.active = false
    self.font = fnt or font
    self.yo = -(self.height - self.font:getHeight()) / 2
    return o
end

and that class has a function called draw(made with Löve2d)

function Edit:draw(  )
    if self.active then
        love.graphics.setColor(255,255,255,255)
     love.graphics.rectangle("fill",self.x,self.y,self.width,self.height)
        love.graphics.setColor(0,0,0,255)
        love.graphics.printf(self.text,self.font,self.x,self.y,self.width, "center",0,1,1,0,self.yo)
    else 
        love.graphics.setColor(255,255,255,255)
        love.graphics.rectangle("line",self.x,self.y,self.width,self.height)
        love.graphics.printf(self.text,self.font,self.x,self.y,self.width, "center",0,1,1,0,self.yo)
    end
end

and in my main i create 2 of them

edit1 = Edit:new(10,10,60,50,"1")
edit2 = Edit:new(80,10,60,50,"2")

and draw them in the callback

function love.draw( )
    edit1:draw()
    edit2:draw()
end

but it only draws edit2? if i switch the places in draw it still only draws edit2 but if i switch their places while creating them in the main it now only draws edit1?

Answer 1

This is the most common beginners mistake when they get into OOP in Lua.

You're assigning all those values to self which is Edit . But if you want to change your instance you need to assign them to o .

Otherwise each call to Edit.new will overwrite the values.

The second problem is that your instance o is a global. You need it to be local. Or you will overwrite your instances each time.

 function Edit:new (x,y,w,h,text,fnt)
      local o = {}   
      setmetatable(o, self)
      self.__index = self
      o.x = x or 0
      o.y = y or 0 
      -- and so forth
      return o
    end

Read this:

https://www.lua.org/pil/16.html

http://lua-users.org/wiki/ObjectOrientedProgramming

Answer 2

You initiates your object not quite correct.

In new function you initiates your object and self in this function is your metatatable.

The other problem that you creates global object o .

So your new function must be:

function Edit:new(x,y,w,h,text,fnt)
    local o = {}
    setmetatable(o, self)
    self.__index = self
    o.x = x or 0
    o.y = y or 0
    o.width = w or 10
    o.height = h or 10
    o.text = text or ""
    o.active = false
    o.font = fnt or font
    o.yo = -(o.height - o.font:getHeight()) / 2
    return o
end