Beginner question - self:addChild

bvarhegyi

In the Gideros game development book there is an example on page 50.

It looks like this.

Button = Core.class(Sprite)

function Button:init()
self:addChild(sprite)
end

local bitmap=Bitmap.new(Texture.new("images/balls.png", true))
local btn = Button.new(bitmap)
stage:addChild(btn)
btn:setPosition(100,100)

However this results in an error message:
main.lua:4: bad argument #1 to 'addChild' (Sprite expected, got nil)
stack traceback:
main.lua:4: in function 'init'
[string "property.lua"]:52: in function '__new'
[string "property.lua"]:59: in function 'new'
main.lua:8: in main chunk

Why?
If I leave out the that self:addChild, then it compiles but nothing is rendered.

bvarhegyi

What I do not understand apart from error message:
- Why do I need the addChild, even when Button is derived from a Sprite class?

ar2rsawseen

@bvarhegyi the real code is (copied from the book)

function Button:init(sprite) self:addChild(sprite) end

So it is some other sprite that you pass to Button constructor and add it to button as a child

bvarhegyi

My bad!! Thx a lot!