Move Phase Touch Error

Getting Started Newbie Questions
#1

Hi all, I am new to Corona and am trying to get a hang of why I am getting certain errors.

I have a game that involves dragging an object around the screen, but the touch does not have to occur on the object directly. After reading through other posts I am able to drag the object by directly touching it, but when I try to implement code to do so when touching a different part of the screen I get the error “attempt to perform arithmetic on field ‘markX’ (a nil value)”

Here is my code, which is set in the scene:create(event) space.

local ball = display.newCircle(WIDTH\*.2,HEIGHT\*.2,WIDTH/80) physics.addBody(ball,{density=1.0, friction=0.5, bounce=0.4, radius=WIDTH/80, filter = ballCollisionFilter}) local touchSensor = display.newRect(0,0,WIDTH,HEIGHT) touchSensor.isVisible = false touchSensor.isHitTestable = true local function ballTouch(event) if event.phase == "began" then self.markX = self.x -- store x location of object self.markY = self.y elseif event.phase =="moved" then local x = (event.x - event.xStart) + self.markX local y = (event.y - event.yStart) + self.markY ball.x, ball.y = x, y end return true end touchSensor:addEventListener("touch", ballTouch) 

I am not sure why this error occurs as the self.markX and self.markY variables work when the touch event is on the “ball” object itself.

Thanks in advance for any replies.

#2 
 local function ballTouch( self, event) if event.phase == "began" then self.markX = self.x -- store x location of object self.markY = self.y elseif event.phase =="moved" then local x = (event.x - event.xStart) + self.markX local y = (event.y - event.yStart) + self.markY ball.x, ball.y = x, y end return true end touchSensor.touch = ballTouch touchSensor:addEventListener("touch")
#3

roaminggamer, thanks for the solution. Sorry for my slow response I created more issues on my own I had to resolve before I could implement your help.

#4 
 local function ballTouch( self, event) if event.phase == "began" then self.markX = self.x -- store x location of object self.markY = self.y elseif event.phase =="moved" then local x = (event.x - event.xStart) + self.markX local y = (event.y - event.yStart) + self.markY ball.x, ball.y = x, y end return true end touchSensor.touch = ballTouch touchSensor:addEventListener("touch")
#5

roaminggamer, thanks for the solution. Sorry for my slow response I created more issues on my own I had to resolve before I could implement your help.