whats wrong with this code? (very short)

Harrison

whats wrong with this code?
i was follwing along with ar2rsawseen's book,and this happened:


print("hello world")
local texture = Texture.new("images/ball.png")
local image = Bitmap.new(texture)
image:setPosition(40,40)
stage:addChild(image)
local shape = Shape.new()
shape:setLineStyle(5, 0Xff0000,1)
shape:setFillStyle(Shape.SOLID,0x000ff,0.5)
Shape:beginPath()
Shape:moveTo(0,0)
shape:lineTo(0,100)
shape:lineTo(100,100)
shape:lineTo(100,0)
shape:closePath()
shape:endPath()
shape:setPosition(40,40)
stage:addChild(shape)

returns:

main.lua:5: calling 'beginPath' on bad self (Shape expected, got table)
stack traceback:
main.lua:5: in main chunk
main.lua:9: calling 'beginPath' on bad self (Shape expected, got table)
stack traceback:
main.lua:9: in main chunk
main.lua:9: calling 'beginPath' on bad self (Shape expected, got table)
stack traceback:
main.lua:9: in main chunk

it could be the book, but its probably me and my bad copying skills )

eezing

The 's' in your object is lowercase here:

local shape = Shape.new()

but the 's' is uppercase here:

Shape:beginPath()
Shape:moveTo(0,0)

Either this is a typo or you might not fully understand the concept. Post if you need help with the concept.

Harrison

i tried to fix it... but
print("hello world")
local texture = Texture.new("images/ball.png")
local image = Bitmap.new(texture)
image:setPosition(40,40)
stage:addChild(image)
local shape = Shape.new()
shape:setLineStyle(5, 0Xff0000,1)
shape:setFillStyle(Shape.SOLID,0x0000ff,0.5)
shape:beginPath()
shape:moveTo(0,0)
shape:lineTo(0,100)
shape:lineTo(100,100)
shape:lineTo(100,0)
shape:closePath()
shape:endPath()
shape:setPosition(40,40)
Stage:addChild(shape)
results in:
main.lua:17: index '__userdata' cannot be found
stack traceback:
main.lua:17: in main chunk

petec

You've now got an uppercase 'S' on 'stage' in the final stage:addChild(shape). Is that the problem?

thanhquan1512

maybe "stage" instead of "Stage"?

Harrison

ahh.. so when i write something it should be lowercaseUppercaseUppercase etec.
thanks guys!

Mells

@Harrison
you should explore the concept of classes (Stage, Shape > Those names are defined) and instances of classes (stage, shape > You can name it however you want).

This article on Lua Naming conventions might help also.

you could have the following:

local myShape = Shape.new()

if you want.

The confusion might come from the fact that in Gideros stage is an instance of Stage that is already available for you so you can not user another name.
Probably something like this is happening behind the scenes :

stage = Stage.new(parameters)

Same for :

application = Application.new(parameters)

Once multi stages are available (as discussed by Atilim a while ago) you will probably have the ability to do :

myStage1 = Stage.new(parameters) myStage2 = Stage.new(parameters)

---

In books, I like when they use specific names to show that the user has freedom to name his variables.
Your code would be :

-- ############################### -- DONE FOR YOU BY GIDEROS. DON'T DO IT. HERE FOR CLARIFICATION -- -> stage = Stage.new() -- ###############################   -- Create myImage local myTexture = Texture.new("images/ball.png") local myImage = Bitmap.new(myTexture) myImage:setPosition(40,40) stage:addChild(myImage)   -- Create myShape local myShape = Shape.new() myShape:setLineStyle(5, 0Xff0000,1) myShape:setFillStyle(Shape.SOLID,0x0000ff,0.5) myShape:beginPath() myShape:moveTo(0,0) myShape:lineTo(0,100) myShape:lineTo(100,100) myShape:lineTo(100,0) myShape:closePath() myShape:endPath() myShape:setPosition(40,40) stage:addChild(myShape)

Does that help to clarify?

Other devs with more experience might correct me if I'm wrong / or if more clarifications are need.

Harrison

yeah, thanks. that is perfect.

Mells

last thing, you can use

< pre lang="lua" >your code here< /pre >

to have your code formatted (remove spaces).
It's easier to for us to scan your code that way, and for you to get quick and relevant answers.