attempt to call method 'draw' a nil value

[RonanZero]

In my unit code, I have this:

Code: Select all

function unit:draw()
	love.graphics.draw(unit.img, unit.x, unit.y)
end

And I call it in love.draw() like this:

Code: Select all

for i, unit in ipairs(units) do
			unit:draw()
		end

It says attempt to call method 'draw' a nil value

Oh and, yes, unit code is being loaded, obviously. And unit is a table with x, y, hp, stuff like that in it.

EDIT: Might as well put the whole unit code, since I get an error on unit:draw func anyway, about x/y being tables not numbers... here it is... help me fix dis too

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units = {}
unit = {
	x = {},
	y = {},
	speed = 100,
	color = "255, 255, 255",
	hp = 40,
	img = love.graphics.newImage("resource/unit_green.png"),
	laserdmg = 10
}

function unit.create(xpos, ypos)
table.insert(unit.x, xpos)
table.insert(unit.y, ypos)
units[#units+1] = {x=xpos, y=ypos}
end

function unit:draw()
	love.graphics.draw(unit.img, unit.x, unit.y)
end

function unit:update(dt)

end

[ArchAngel075]

instead try

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 for i, unit in pairs(units) do
  unit:draw()
 end

(Ive only really worked with pairs() and not ipairs)


next im not sure about how you instantiate your units with unit.Create, ive only ever used:

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 object:new()
  local o = {}
  setmetatable(o, self)
  self.__index = self
  return o
 end

and more recently a larger function to allow inheritance....

[zorg]

Love complains because unit.x and unit.y are tables, not numbers.
The thing is, you don't even need those tables since you save the x and y in the units table anyway. The code

Code: Select all

function unit:draw()
    love.graphics.draw(unit.img, units.x, units.y

would work, but you don't iterate over all the units with that, so:

Code: Select all

function unit:draw()
    for i,v in ipairs(units) do
        love.graphics.draw(unit.img, v.x, v.y)
    end
end

I did assume that you wanted to use the same image for all of them.

[davisdude]

You could use pairs, but ipairs would work better because of how the table is made.
Also, don't forget things like:

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units = {}
unit = {}
unit.__index = unit
setmetatable( unit, units )

function unit.create(x, y)
	local new = {x=x, y=y}
	new.__index = new
	setmetatable( new, unit )
	return new
end
	
function unit:draw()
	love.graphics.circle( 'fill', self.x, self.y, 2 )
end

-- Example:
function love.load()
	new = unit.create( 32, 32 )
end

function love.draw()
	new:draw()
end

[zorg]

of course, you do not need to use metatables for something simple:

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local units = {}

local draw = function(self)
    love.graphics.circle( 'fill', self.x, self.y, 2 )
end

local update = function(self,dt)
    -- meh
end

local unit = {}

function unit.create(x, y)
   local new = {x=x, y=y}
   new.draw = draw
   new.update = update
   units[#units+1] = new
   return new
end

-- Example:
function love.load()
   new = unit.create( 32, 32 )
end

function love.draw()
   --new:draw() -- this would work too
   for i,v in ipairs(units) do
      v:draw()
   end
end

function love.update(dt)
   --new:update(dt) -- this would work too
   for i,v in ipairs(units) do
      v:update(dt)
   end
end

[davisdude]

True. You don't have to use metatables, they have their pros and cons:
Pros:
- Less typing (if you have lots of functions, you don't need to make a value for them each time).
- Less memory (since the table variables are created each time, it takes more memory. Probably not substantial, but when it matters, it could help).

Cons:
- Makes code a bit more complicated.
- Possible confusion due to multiple functions with the same name.

Can't think of any others, but I'm sure there are more. In general, in my opinion, it's a good practice to use metatables.