Attempt to index a nil value

sLKz

I'm getting the following error:
classes/stack.lua:38: attempt to index field 'element' (a nil value)
stack traceback:
classes/stack.lua:38: in function 'removeSprite'
classes/stack.lua:77: in function

Here is the code:

stack = Core.class(Sprite)   function stack:init(_elementsSize, _cubeSize, _positionX, _positionY) elementsSize = _elementsSize cubeSize = _cubeSize   positionX = _positionX positionY = application:getContentHeight() - _positionY   self.element = {}   index = 1 end   function stack:addSprite(sprite) if index <= elementsSize then self.element[index] = sprite   if index >= 2 then self.element[index - 1]:removeEventListener(Event.MOUSE_DOWN, self.onMouseDown, self.element[index - 1]) self.element[index - 1]:removeEventListener(Event.MOUSE_MOVE, self.onMouseMove, self.element[index - 1]) self.element[index - 1]:removeEventListener(Event.MOUSE_UP, self.onMouseUp, self.element[index - 1]) end   self.element[index]:addEventListener(Event.MOUSE_DOWN, self.onMouseDown, self.element[index]) self.element[index]:addEventListener(Event.MOUSE_MOVE, self.onMouseMove, self.element[index]) self.element[index]:addEventListener(Event.MOUSE_UP, self.onMouseUp, self.element[index])   self.element[index]:setPosition(positionX, positionY - index * 55)   self:addChild(self.element[index])   index = index + 1 end end   function stack:removeSprite() self: removeChild(self.element[index])   index = index - 1   self.element[index]:addEventListener(Event.MOUSE_DOWN, self.onMouseDown, self.element[index]) self.element[index]:addEventListener(Event.MOUSE_MOVE, self.onMouseMove, self.element[index]) self.element[index]:addEventListener(Event.MOUSE_UP, self.onMouseUp, self.element[index]) end   function stack:onMouseDown(event) if self:hitTestPoint(event.x, event.y) then self.isFocus = true   self.x0 = event.x self.y0 = event.y   event:stopPropagation() end end   function stack:onMouseMove(event) if self.isFocus then local dx = event.x - self.x0 local dy = event.y - self.y0   self:setX(self:getX() + dx) self:setY(self:getY() + dy)   self.x0 = event.x self.y0 = event.y   event:stopPropagation() end end   function stack:onMouseUp(event) if self.isFocus then if (event.x > 150) or (event.x < 100) then print("yes") self:removeSprite() end   self.isFocus = false   event:stopPropagation() end end

ar2rsawseen

@sLKz in your code you don't add event listeners to your stack class, but only to stack.elements.
self.elements would onyl be reachable if you added mouse events like this:

function stack:addSprite(sprite) self:addEventListener(Event.MOUSE_DOWN, self.onMouseDown, self) self:addEventListener(Event.MOUSE_MOVE, self.onMouseMove, self) self:addEventListener(Event.MOUSE_UP, self.onMouseUp, self) end