Newbie stuck with timer to remove display object

Getting Started Newbie Questions
#1

Hi,

I’m just starting to use Corona and I’m stuck trying to use removeSelf( ) with a timer.

I’m trying to simulate the blade effect in Fruit Ninja. I create a display object called “rollerpoint” and I want to remove it after 400 milliseconds, but I don’t get it to work. I got pen.lua:32: attempt to index upvalue ‘rollerpoint’ (a nil value).

I haven’t found a way to fix this. Can anyone help me out please. I attach my code.

Cheers!

[lua]local pen = {}

local rollerpoint

pen.rollerpoint = rollerpoint

local color = {1,1,1}

pen.color = color

local lastX = 0

pen.lastX = lastX

local lastY = 0

pen.lastY = lastY

local distBetween = function ( x1, y1, x2, y2 ) – distance between 2 points
local xFactor = x2 - x1
local yFactor = y2 - y1
local dist = math.sqrt( (xFactor*xFactor) + (yFactor*yFactor) )
return dist
end

pen.distBetween = distBetween

local destroy = function( event )
print( “listener called” )
rollerpoint:removeSelf( )
rollerpoint = nil

end

pen.destroy = destroy

local draw = function(target)

local drawing = function(event)

if ( event.phase == “began”) then
–code executed when the player touches the background
print( “bg touched = “…tostring(event.x)…”,”…tostring(event.y) ) --‘event.target’ is the touched object
lastX = event.x
lastY = event.y

elseif (event.phase == “moved”) then

rollerpoint = display.newImageRect( “images/bgs/pen.png”, 40, 7 )
rollerpoint.fill = {color}
rollerpoint:rotate( math.deg(math.atan2(event.y - lastY, event.x - lastX )) ) --it gets the angle between 2 points.
rollerpoint.width = distBetween(lastX, lastY , event.x, event.y)
–transition.to( rollerpoint, {time = 0, xScale = rollerpoint.width * .32} )
transition.to( rollerpoint, {time = 400, height = .1} )
rollerpoint.x = (event.x + lastX) / 2
rollerpoint.y = (event.y + lastY) / 2
lastX = event.x
lastY = event.y
timer.performWithDelay( 400, destroy )

end

end

target:addEventListener( “touch”, drawing ) --add a “touch” listener to playBtn
end

pen.draw = draw

return pen[/lua]

#2

It’s saying that the error is on line 32, so before you even try to remove it. That would imply that line 31 is not successful:

rollerpoint = display.newImageRect( "images/bgs/pen.png", 40, 7 )

My guess would be that there is a typo in the file name “images/bgs/pen.png”. Corona is case sensitive, so double check that the path name exactly matches the real directory + file names.

e.g. If your folder is called “BGS” then it will not work as it is upper case and the path name in your code is lower case)

#3

Thanks Alan.

I already solved it. It turned out to be an scope problem. I leave my corrected code here in case anybody needs to use the Fruit Ninja blade effect in one game.

[lua]local UI = require(“UI”)

local pen = {}

local rollerpoint

pen.rollerpoint = rollerpoint

–local color = { math.random(10)/10 , math.random(10)/10 , math.random(10)/10 }

–pen.color = color

local lastX = 0

pen.lastX = lastX

local lastY = 0

pen.lastY = lastY

local distBetween = function ( x1, y1, x2, y2 ) – distance between 2 points
local xFactor = x2 - x1
local yFactor = y2 - y1
local dist = math.sqrt( (xFactor * xFactor) + (yFactor * yFactor) )
return dist
end

pen.distBetween = distBetween

local destroy = function ( object )

local function remove( … )
object:removeSelf( )
object = nil
end
timer.performWithDelay( 300, remove )
end

pen.destroy = destroy

local draw = function(target)

local drawing = function(event)

if ( event.phase == “began”) then
–code executed when the player touches the background
print( “bg touched = “…tostring(event.x)…”,”…tostring(event.y) ) --‘event.target’ is the touched object
lastX = event.x
lastY = event.y

elseif (event.phase == “moved”) then
rollerpoint = display.newImageRect( “images/bgs/pen.png”, 40, 7 )
rollerpoint:setFillColor( UI.settings.penColor[1],UI.settings.penColor[2],UI.settings.penColor[3] )
rollerpoint:rotate( math.deg(math.atan2(event.y - lastY, event.x - lastX )) ) --it gets the angle between 2 points.
rollerpoint.width = distBetween(lastX, lastY , event.x, event.y)
–transition.to( rollerpoint, {time = 0, xScale = rollerpoint.width * .32} )
transition.to( rollerpoint, {time = 400, height = .1} )
rollerpoint.x = (event.x + lastX) * .5
rollerpoint.y = (event.y + lastY) * .5
lastX = event.x
lastY = event.y
destroy(rollerpoint)
end

end
target:addEventListener( “touch”, drawing )
end

pen.draw = draw

return pen
[/lua]

#4

It’s saying that the error is on line 32, so before you even try to remove it. That would imply that line 31 is not successful:

rollerpoint = display.newImageRect( "images/bgs/pen.png", 40, 7 )

My guess would be that there is a typo in the file name “images/bgs/pen.png”. Corona is case sensitive, so double check that the path name exactly matches the real directory + file names.

e.g. If your folder is called “BGS” then it will not work as it is upper case and the path name in your code is lower case)

#5

Thanks Alan.

I already solved it. It turned out to be an scope problem. I leave my corrected code here in case anybody needs to use the Fruit Ninja blade effect in one game.

[lua]local UI = require(“UI”)

local pen = {}

local rollerpoint

pen.rollerpoint = rollerpoint

–local color = { math.random(10)/10 , math.random(10)/10 , math.random(10)/10 }

–pen.color = color

local lastX = 0

pen.lastX = lastX

local lastY = 0

pen.lastY = lastY

local distBetween = function ( x1, y1, x2, y2 ) – distance between 2 points
local xFactor = x2 - x1
local yFactor = y2 - y1
local dist = math.sqrt( (xFactor * xFactor) + (yFactor * yFactor) )
return dist
end

pen.distBetween = distBetween

local destroy = function ( object )

local function remove( … )
object:removeSelf( )
object = nil
end
timer.performWithDelay( 300, remove )
end

pen.destroy = destroy

local draw = function(target)

local drawing = function(event)

if ( event.phase == “began”) then
–code executed when the player touches the background
print( “bg touched = “…tostring(event.x)…”,”…tostring(event.y) ) --‘event.target’ is the touched object
lastX = event.x
lastY = event.y

elseif (event.phase == “moved”) then
rollerpoint = display.newImageRect( “images/bgs/pen.png”, 40, 7 )
rollerpoint:setFillColor( UI.settings.penColor[1],UI.settings.penColor[2],UI.settings.penColor[3] )
rollerpoint:rotate( math.deg(math.atan2(event.y - lastY, event.x - lastX )) ) --it gets the angle between 2 points.
rollerpoint.width = distBetween(lastX, lastY , event.x, event.y)
–transition.to( rollerpoint, {time = 0, xScale = rollerpoint.width * .32} )
transition.to( rollerpoint, {time = 400, height = .1} )
rollerpoint.x = (event.x + lastX) * .5
rollerpoint.y = (event.y + lastY) * .5
lastX = event.x
lastY = event.y
destroy(rollerpoint)
end

end
target:addEventListener( “touch”, drawing )
end

pen.draw = draw

return pen
[/lua]