Button Class Question ?

Code Sharing
1

Hi i found this code here On this page, and iam New in Programming. I Test this code in codea of my ipad 3.
The Error is: error: [string "Button = class() … 24: attempt to Index Field ‘Position’ a Nil Value

Here is this code: File 1: MAIN

-- Use this function to perform your initial setup
function setup()
    print("Hello World!")
    button = Button("Planet Cute:Chest closed","PlanetCute:Cest Open",WIDTH/2, HEIGHT/2 )
    button.Action = function() buttonPressed() end
end



    
-- This function gets called once every frame
function draw()
    -- This sets a dark background color 
    background(40, 40, 50)
    Button:draw()
end

function ButtonPressed()
    print"Button pressed"
end

function touched(touch)
    Button:touched(touch)
end



File 2: Button

Button = class()


function Button:init(btnNormal,btnSelect,x,y)
        self.Position = vec2(x,y)
        self.btnNormal = btnNormal
        self.btnSelect = btnSelect
        self.Selceted = false
        self.Action = nil
        self.Width,self.Height = spriteSize(self.btnNormal)
      end

function Button:draw()
    if self.Selceted == true then
        sprite(self.btnSelect,self.Position.x,self.Position.y,self.Width,self.Height)
    elseif self.Selcetet == false then
        sprite(self.btnNormal,self.Position.x,self.Position.y,self.Width,self.Height)
    end
end


function Button:touched(touch)
    if touch.state == BEGAN or touch.state == MOVING then
        if math.abs(self.Position.x - touch.x) <= (self.Width/2)
       and math.abs(self.Position.y - touch.y) <= (self.Hight/2) then 
        self.Selected = true
    else
        self.Selceted = false
    end
    elseif touch.state == ENDED then  
        if self.Selected  == true and self.Action then 
        self.Action()
    end
    self.Selected = false
    end
end

He Can Not Show my Button , while Not the correct Position, but when i give x and y 200 and 200 it is also Nil.
I Hope One Guy Can me help what is my misstake.
Thank you.

2

@Striker_der_Echte For starters, you should put 3 ~ before and after your code so it formats correctly. Then you need to change Button:draw() to button:draw() and Button:touched(touch) to button:touched(touched).

3

Some of the words are not spelled right, but I just made them the same spelling. Here is a working version.


-- Use this function to perform your initial setup 
function setup()
    print("Hello World!") 
    button = Button("Planet Cute:Chest Closed","Planet Cute:Chest Open",
        WIDTH/2, HEIGHT/2 ) button.Action = function() ButtonPressed() end 
end

-- This function gets called once every frame
function draw() -- This sets a dark background color 
    background(40, 40, 50) 
    button:draw()
end

function ButtonPressed() 
    print"Button pressed" 
end

function touched(touch) 
    button:touched(touch) 
end

Button = class()

function Button:init(btnNormal,btnSelect,x,y) 
    self.Position = vec2(x,y) 
    self.btnNormal = btnNormal 
    self.btnSelect = btnSelect 
    self.Selceted = false 
    self.Action = nil 
    self.Width,self.Height = spriteSize(self.btnNormal) 
end

function Button:draw() 
    if self.Selceted == true then   
        sprite(self.btnSelect,self.Position.x,self.Position.y,self.Width,self.Height) 
    elseif self.Selceted == false then 
        sprite(self.btnNormal,self.Position.x,self.Position.y,self.Width,self.Height)
    end
end

function Button:touched(touch) 
    if touch.state == BEGAN or touch.state == MOVING then 
        if math.abs(self.Position.x - touch.x) <= (self.Width/2) and 
                math.abs(self.Position.y - touch.y) <= (self.Height/2) then 
            self.Selceted = true
        else 
            self.Selceted = false 
        end 
    elseif touch.state == ENDED then
        if self.Selceted == true and self.Action then 
            self.Action() end self.Selected = false 
        end 
end
4

Thank You Dave1707 :slight_smile: :slight_smile: i have found 5 error in my Code. And i Think i have Zero :-S

But 1. Question?

But i dont why must it the Class (Big B) Button:draw() and in the Main (small b) button:draw()
The Same is like Button: touched(touch) in the Class Funktion is it Name (Big B). And in the Main when it Recall my Class funktion it must Small b button:touched(touch) ???

This is Not logical for me.

:((

5

And Very Big Thank you 4 the RIGHT CODE.

6

The class is named Button, so all functions for that class must be defined using Button. In Main, you are creating an instance of the class named button, so each function for that instance must be called using button. If your instance of the class was created as myButton in Main, then you would call myButton:draw() to draw it and myButton:touched(touch) to handle it being touched.

7

@Striker_der_Echte Button is the class name. When you want to get an instance of that class, you assign it to a variable. That’s what’s done in setup() with the line button=Button(…). The variable “button” now refers to the Button code. So to call the Button draw() function you use button:draw(). Same goes for the Button touched() function. You use button:touched(). You could also use xyz=Button(…) . Then you would use xyz:draw() and xyz:touched(). The code used by “button” and “xyz” are different instances of the Button code and would work as seperate Buttons. You could use the Button code for as many buttons as you want to draw. You would just assign different locations for each button when you assign it to a different variable.